HYGIENE OF WATER AND WATER SUPPLY OF POPULATED AREAS. EVALUATION OF THE QUALITY OF DRINKING WATER. METHODS OF IMPROVING THE QUALITY OF DRINKING WATER.HYGIENE OF SOIL AND CLEANING INHABITED PLACES

Water is vital to humans. It is needed for food preparation, drinking, washing, and irrigation. In addition, massive quantities are used daily in industrial processes. Yet, it is a limited resource that must be collected and distributed with increasing care. The most important source of water is rain, which may be collected directly in cisterns and reservoirs or indirectly through a watershed system or well. A watershed is the network of rivulets, streams, and rivers by which entire areas are watered. Ground water is rain that has trickled through rock layers, forming pools after many years. If it is under pressure, groundwater may bubble to the surface as a spring. Irrigation canals, reservoirs, wells, and water towers are man-made devices for diverting and collecting water from these natural sources. Because of contamination concerns, water from reservoirs, wells, and rivers is usually processed in a treatment plant before distribution.

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The ultimate source of all natural potable water on the earth is rain, which is rarely used as a direct source except on islands in salt water, such as Bermuda, where the rain is collected and led into cisterns to serve as the only available water supply. When rain falls, it runs off into streams, in the case of heavy rains, or soaks into the ground, percolating through porous strata until it reaches an impervious stratum, upon which it collects, forming groundwater. Groundwater is the source of wells and of the springs that feed streams, rivers, and lakes. In its course, groundwater dissolves soluble mineral matter, and often the surface waters of rivers and lakes are polluted by the influx of sewage or industrial wastes (see Sewage Disposal; Water Pollution). In modern water-supply systems, an entire watershed is usually made into a reservation to control pollution. The waters are impounded by a system of dams, and flow by gravity, or are pumped, to the local distribution system.

Water is Essential for Life

It covers 71% of the earth's surface and makes up 65 % of our bodies. Everyone wants clean water-- to drink, for recreation, and just to enjoy looking at. If water becomes polluted, its loses its value to us economically and aesthetically, and can become a threat to our health and to the survival of the fish living in it and the wildlife that depends on it.

Hygienic significance of water

Water physiological functions:

-       flexibility – about 65 % of body mass of adult person consists of water. 70 % of water is the intracellular water, 30 % - extracellular water (in blood), (7%) - lymph and 23 % - intertissue fluid. Water makes up 20 % of the bone mass, 75 %, of the muscle mass, 80% of the connective tissue mass, 20% of blood plasma mass, 99% of vitreous body of an eye. Major part of water is a component of macromolecular complexes of proteins, carbohydrates and fats, forming the jelly-like colloid cells and extracellular structures together with them. The smaller part of it is in a free state;

-       participation in metabolism and interchange of energy – all assimilation and dissimilation processes in organism occur in water solutions;

-       role in support of osmotic pressure and acid-base balance;

-       participation in heat exchange and thermoregulation – at evaporation of 1 g of moisture from lungs’ surface, mucous membranes and skin (latent heat of evaporation) organism loses 2.43 kJ (0.6 kcal) of heat;

-       transportation function – delivery of nutrients to cells with blood and lymph, removal of waste products from the organism with urine and sweat;

-       as a component of dietary intake and a source of macro- and microelements supply to organism;

-       there are neuropsychic disorders that are resulted from impossibility to satisfy thirst if water is not available or if it is of bad organoleptic characteristics. According to I.P. Pavlov’s doctrine on higher nervous activity, odour, taste, after-taste, water appearance, clarity (transparency) and colour are irritators that influence the whole organism through central nervous system. Worsening of organoleptic characteristics of water causes the reflex effect on water intake schedule and some physiological functions, for example it oppresses the secretory function of stomach. Drinking of such water causes the defence reaction in human organism – the feeling of aversion, which makes a person to refuse such water irrespective of thirst.

Epidemiological and toxicological role of water

Water can participate in spread of infections in the following ways:

-       as transfer factor of pathogens with the fecal-oral transfer mechanism: enteric infections of bacterial and viral origin (typhoid, paratyphoid А, В, cholera, dysentery, salmonellosis, coli-entheritis, tularaemia /deep-fly or rabbit fever/, viral and epidemic hepatitis А, or Botkin disease, viral hepatitis E, poliomyelitis and other enterovirus diseases, such as Coxsakie, EСНО etc.); geohelminthosis (ascaridiasis, trichocephaliasis, ankylostomiasis); biohelminthosis (echinococcosis, hymenolepiasis); of protozoal etiology (amebic dysentery (amebiasis), lambliasis); zooanthroponosis (tularemia, leptospirosis and brucellosis);

-       as a transfer factor of pathogens of the skin and mucous membrane diseases (when swimming or having another contact with water): trachoma, leprosy, anthrax, contagious molluscum, fungous diseases (i.e., epidermophytosis);

-       as the habitat of disease carriers – anopheles mosquitoes, which transfer malarial haemamoeba and others (open water reservoirs).

Symptoms of water epidemics:

-       simultaneous appearance of big number of enteric infected people, i.e. jump of population morbidity – so-called epidemic outburst;

-       people who used the same water source, the same pipeline of water supply network, the same water-pump, shaft well etc. will suffer from diseases;

-       morbidity level will stay high for the long period of time to the extent of water contamination and consumption;

-       morbidity curve will have one, two, three, or more peaks. First of all those diseases that have short incubation period will be registered (coli-entheritis, salmonellosis - 1-3 days, cholera – 1-5 days, typhoid – 14-21 days and at last - those with the longest period: virus and epidemic hepatitis А and Е – 30 days and more);

-       after the taking of antiepidemic measures (liquidation of the contamination source, disinfection of water supply network, sanitation of wells) the outburst fades away and morbidity goes down drastically;

-       still, for some time morbidity remains above the sporadic level – so-called epidemic tail. This is caused by the appearance of big amount of new potential sources of infection (sick people and infection carriers) during the epidemic outburst and activation of other ways of the pathogenic microorganisms spreading from these sources – domestic contact (through dirty hands, dishes, children toys, personal hygiene articles), through food or by living carriers (flies) etc.

Toxicological role of water consists in it containing chemical agents that may negatively influence people health causing different diseases. They are divided into chemical agents of natural origin, those, which are added to water as reagents and chemical agents, which come into the water as the result of industrial, agricultural and domestic pollution of water supply sources. Insufficient or non-effective treatment of such waters at waterworks procures the continuous toxic effect of small concentrations of chemical agents, or, rarely, in cases of accidents and other emergency situations – acute poisonings.

Balneal role of water

 Water is used in medicinal purpose for rehabilitation of convalescents (drinking of mineral waters, medicinal baths), and also as tempering factor (bathing, swimming, rub-down).

Domestic and economic role of water

 Sanitary-hygienic and domestic functions of water include:

-       water usage for cooking and as a part of dietary intake;

-       usage of water as means of keeping body, clothes, utensil, residential and public premises and industrial areas, settlements clean;

-       watering of the green areas within settlements;

-       sanitary-transport and disinfection functions of water – disposal of residential and industrial waste through sewer system, waste processing on plants, self-purification of water reservoirs;

-       fire fighting, atmospheric pollution clearing (rain, snow).

Economical functions of water:

-       usage in agriculture (irrigation in crop and gardening, greenhouses, poultry and cattle breeding farms);

-       industry (food, chemical, metallurgy etc.);

-       as the route of passenger and cargo transportation.

Classification of water supply sources

 Water supply sources are divided into ground and surface:

-      middle waters with pressure (artesian) and without pressure that lie in aquifers (water-bearing horizons,) (sandy, gravelled, cracked) between impermeable to water layers of soil (clay, granites), therefore safely protected from penetration of pollutants from the surface. Middle water replenishes in feeding zones – places, where the auriferous stratum pinches out onto the surface, located considerably far away from the water take point. Middle waters are characterized by not very high, stable temperature (5-12°С), constant physical and chemical composition, steady level and considerable flow; they contain almost no microorganisms, especially pathogenic. Such waters are epidemically safe and don’t require disinfection;

-      underground waters that are located in aquifers above the first impermeable layer of soil and therefore, in case of them lying not very deep, they are insufficiently protected from penetration of pollutants from the surface. They are characterized by seasonal fluctuations of chemical and bacteriological composition and level, flow that depends on frequency and number of precipitations, availability of open-air water reservoirs, depth and soil type. Getting filtrated through the 5-6 m or bigger layer of clean fine-grained soil ground waters become clear, colourless, contain almost no pathogenic microorganisms. Supplies of ground water are small, therefore, in order to use them as a source of centralized water supply, the artificial recharge (replenishment) of them using special technical facilities is required;

-      spring water, flowing out from aquifers that pinch out onto the surface due to descending relief, e. g. on the hill slope, in deep ravine.

- perched groundwater, lying next to the ground surface, is formed as a result of atmospheric precipitates filtration within a small area. Very small supplies and bad water quality do not allow recommending perched groundwater as the source of domestic and drinking water supply.

Surface waters are divided into flowing (running) waters (rivers, waterfalls, glaciers), stagnant (dead-water, still water) (lakes, ponds, artificial open water reservoirs). Their water composition depends much on the soil at the territory of water intake, hydrometeorological conditions, and varies sufficiently during the year depending on the season or even on the weather. Compared to ground waters, surface water sources are characterized by big amount of suspended substances, low clarity, higher colour due to humic substances that are washed away from the soil, higher content of organic compounds, presence of autochthonic microflora and dissolved oxygen. Open-air reservoirs can easily be polluted from outside, therefore, from epidemiological point of view they are potentially unsafe.

In some water-poor or arid areas, the imported and precipitation (atmospheric) water (rain, snow), which is stored in indoor water reservoirs or artificially filled wells, is used.

The best is the situation when quality of water in the source of water supply completely meets the contemporary criteria of the good water quality. Such water doesn’t require any treatment and the only concern is not to spoil its quality at the stages of its take from the source and delivery to consumers. But disinfection of such water is the part of sanitary requirements anyway. Only some underground middle waters are like this, mostly – artesian (pressure) waters. In all other cases water in the source, especially the surface water, requires quality improvement: lowering of suspended materials concentration (clearing) and colour (decolouration), getting rid of pathogenic and conditionally pathogenic microorganisms (disinfection), sometimes chemical composition improvement using special treatment techniques (desalination, softening, defluorination, fluorination, deferrization etc.). Hygienic requirements to water quality in sources of centralized water supply are given in appendix 4.

Sources of the surface water reservoirs pollution

The main source of pollution of surface water reservoirs are sewage waters (especially untreated or insufficiently treated water) that are created as the result of the water use in private life, industry, poultry and cattle factories etc. Partial pollution of water reservoirs occurs in the result of surface drainage of rain, storm waters and waters that appear during snow melting. Sewage waters and surface drainage add a big amount of suspended solids and organic compounds to water of reservoirs that results in more colour and water turbidity increase, clarity (transparency) lowering, oxidation and biochemical oxygen demand (BOD) increase, amount of dissolve oxygen lowers, concentration of nitrogen-containing substances and chlorides increases, bacterial insemination grows. Together with industrial wastewaters and sewage from farmlands, as it was mentioned before, various hazardous toxic chemical substances get into water reservoirs.

Water in open reservoirs may be polluted in the result of its use for transport purposes (passenger, freight shipping, timber floating), when working near river-beds (e.g., extraction of river sand), during watering animals, at sports competitions, recreation of population.

Self-purification (natural purification) of open-air water reservoirs

Self-purification (natural purification) of open air water reservoirs takes place in the result of various factors’ effect: а) hydraulic(mixing and dilution of pollutants by water of water reservoir); b) mechanical (precipitation/sedimentation of suspended solids); c) physical(solar radiation and temperature effect); d) biological (interaction of water plant organisms and microorganisms with sewage organisms that got into reservoir); e) chemical (elimination of contaminants as the result of hydrolysis); f) biochemical (conversion of some substances into other due to biological elimination, mineralization of organic substances as the result of biochemical oxidation caused by water autochthonic microflora). Natural purification with pathogenic microorganisms occurs due to their death as the result of antagonistic action of water saprophytic organisms, antibiotic substances, bacteriophages etc. In case of pollution of water reservoirs by domestic and industrial wastewaters, processes of natural purification may be stopped. Water in reservoirs becomes overgrown (vegetation burst of aquatic plants, plankton), putretaction of water.

Selection of the source of centralized domestic and drinking water-supply

It is based on two theses:

-       consumer supply with adequate amount of good quality drinking water (water quality in reservoir must be suitable for conversion using up-to-date water treatment methods into potable water of good quality that would meet all requirements of State Standard (2874-82, SSRandN 136/1940) currently in force);

-       control of the highest sanitary reliability of the source (selection of the source is based on assessment and prognosis of its possible pollution).

The source of centralized domestic and drinking water-supply is to be selected as follows: 1) middle water (artesian) aquifers; 2) middle water (not-artesian) aquifer; 3) underground waters, which are refilled artificially; 4) surface waters (rivers, water reservoirs, lakes, canals).

When selecting the source, water amount sufficiency for covering all needs of the built-up area is considered, water supply points (water intakes) are defined and organizational opportunities for sanitary protection zones are assessed.

Hygienic principles are assumed as the basis of selection of water- supply source; water quality requirements of ground and surface sources, selection procedure are represented in SS 2761-84 “Centralized domestic and drinking water supply sources. Hygienic, technical requirements and selection guidelines” (Appendix 4).

Technique of sanitary inspection of water-supply sources

 Sanitary inspection includes three main stages:

-         sanitary-topographic inspection of water source environment;

-         sanitary-technical inspection of condition of water source equipment;

-         sanitary-epidemiological inspection of area of water source location.

Main task of sanitary-topographic inspection of water source is to discover possible sources of water pollution (dumps, refuse pits, lavatories, livestock farms, cemeteries etc.), distances from them to water source, topography of the locality, (drain direction of rain and snow waters towards water source or in another direction, flow direction of ground waters, overflows). On the basis of sanitary-topographic inspection a map – layout of positional relationship of water source and listed objects with marks of distances and direction of locality slope is created.

In most cases relationship between water source and source of pollution may be determined by research. For this purpose a saturated solution of sodium chloride or solution of fluoresceine is poured into the source of pollution (at least one bucket of mixture for every 10 m of distance towards water source), and every 3-4 hours during one or two days chlorides (or fluoresceines) are sampled in the water source.

The purpose of sanitary-technical inspection is to give a hygienic assessment of condition of technical equipment of hydraulic works at water source. Thus, in case of decentralized (local) water-supply, accuracy of allocation and exploitation of the mineshaft (availability and condition of log cabin, awning, riprap, devices for water lifting, “loamy key trench”); in case of centralized water-supply from ground middle water source – accuracy of arrangement and condition of artesian well, water lifting pumps; in case of surface water source – of diversion scoop and coastal sink. In case of centralized water-supply, sanitary-technical condition of main facilities of water-pipe, water supply network and constructions on it (namely, water-pumps).

It is of practical importance to determine the amount of water in the source of water and its discharge (output). E.g. amount of water in the well made of concrete rings with log cabin is determined by the formula:

V = π×R²×h,

where:    V – amount of water in the well, m³;

p - 3.14;

R – radius of log cabin ring, m;

h – water layer height, m.

Water height is determined by cord with weight, which is pulled down till the touch of the bottom and then a wet part of the cord is measured.

To find out discharge (output) of the well, 30-40 buckets of water are pumped out (scooped out) then the change in the level of water is marked and the time during which the previous level of water restores is fixed. Discharge (output) is calculated by formula:

D = 

            where: D – discharge of the well, l/hour;

      V – volume of pumped out water, l;

       t – time, during which the level of water restores and time of water pumping, minutes.

River discharge is the amount or volume of water that flows through a given cross-section of a river in a given unit of time (m/sec)

Discharge (output) of a brook or a small river is calculated by formula:

D = 0.5×b×h×v,

            where:  D – output (productivity), m³/sec;

       b – water flow width, m;

       h – water flow depth at the deepest point, m;

       v – flow velocity, m/sec (is determined using a float and stop-watch).

Sanitary-epidemiological inspection is aimed to discover and consider the following:

-       presence of intestinal infectious diseases (cholera, typhoid, paratyphoid А, В, dysenteries, virus hepatitis etc.) among population, which uses water from this source or lives close to it;

-         presence of epizootic diseases (tularemia, brucellosis, anthrax, murrain, mad cow disease (BSE) etc.) among rodents, domestic animals;

-       sanitary condition of the settlement (pollution of the territory, methods of collection and disinfection of liquid and solid domestic and industrial waste etc.).

During sanitary inspection water samples from open water reservoir, well or artesian well for further laboratory analysis are taken.

Technique of water sampling for laboratory analyses

During water sampling from open reservoir or a well the temperature of water is measured by a special thermometer (Fig. 16.1.) or by an ordinary chemical thermometer, the vessel of which is wrapped up with some layers of gauze bandage. Temperature is taken directly in the water source. Thermometer is put down into the water for 5-8 min., then it is quickly drawn up and temperature is read.

Fig. 1 Thermometer for taking temperature of water in reservoirs and wells (а), bathometers for water sampling for analysis (b).

Water sampling from open reservoirs and wells is carried out using bathometers of different design and supplied by double cord for putting the instrument down to specified depth and for opening the cork of the vessel at that depth (Fig. 1-b).

For water sampling from flowing water reservoirs (river, brook) there is a design of bathometer with stabilizer that directs a neck of the vessel against the stream.

Water sampling from water tap or equipped catchment is carried out:

-      for bacteriological analysis. Sample is put into a sterile bottle of 0.5 l volume, with bulky cork, wrapped with paper cap from above after preliminary singeing of outlet port of the tap or catchment by spirit flame and letting water out from the tap during at least 10 min. In order to avoid bulky cork wetting, only three quarters of the bottle is filled with water to leave at least 5-6 cm of air space under the cork. The bottle with bulky cork is preliminary sterilized in drying box at 160⁰ С during one hour;

-      for short sanitary-chemical analysis (organoleptic criteria, main indices of chemical compound and water pollution). About 1 liter of water is taken into a chemically clean glassware, which was preliminary rinsed with water to be sampled (for complete sanitary-chemical analysis 3-5 l of water are taken off).

During sampling a covering letter is written down. This letter indicates: type, name, location, address of the water source (surface water reservoir, artesian well, mineshaft, catchment, water tap, water-pump); its short specification, weather state during sampling and during last 10 days; reason and goal of sampling (regular inspection, adverse epidemic situation, population complaints about deterioration of water organoleptical properties); laboratory, to which the sample is sent; required extent of examinations (short, full sanitary-chemical analysis, bacteriological analysis, determination of pathogenic microorganisms); date and hour of sampling; research result received during sampling (temperature); who tested (surname, position, institution); signature of an official person, who took the sample.

Samples must be delivered to the laboratory as quickly as possible. Bacteriological analyses must be started during 2 hours since taking samples or in case of keeping samples in refrigerator at 1-8°С at the latest 6 hours. Physical and chemical analysis is made during 4 hours after taking a sample or in case of keeping a sample in refrigerator at 1-8°С at the latest 48 hours. In case of inability to perform the analysis during specified terms, sample must be preserved (except samples for physical-and-organoleptical and bacteriological analyses, and for BOD determination that must be necessarily made during terms specified above). Samples are preserved by 25% of H₂SO₄ - solution on the basis of 2 ml for 1 l of water or by another method depending on factors to be determined.

Taken sample comes with accompanying form, in which one indicates address details, kind of water source, where samples are directed, aim of the analysis, date and time of taking a sample, signature of an official person, which took this sample.

Water is the main substance of biosphere, without which the existence of organic nature is impossible. Water is vital to humans. It is needed for food preparation, drinking, washing, and irrigation. In addition, massive quantities are used daily in industrial processes. Any vital process cannot be performed without water, and any cell cannot exist in anhydrous environment. Water has the importance not only for drinking and meal, and also for normal existence of the human. Yet, it is a limited resource that must be collected and distributed with increasing care.

The most important source of water is rain, which may be collected directly in cisterns and reservoirs or indirectly through a watershed system or well. A watershed is the network of rivulets, streams, and rivers by which entire areas are watered. Ground water is rain that has trickled through rock layers, forming pools after many years. If it is under pressure, groundwater may bubble to the surface as a spring. Irrigation canals, reservoirs, wells, and water towers are man-made devices for diverting and collecting water from these natural sources. Because of contamination concerns, water from reservoirs, wells, and rivers is usually processed in a treatment plant before distribution.

Because of enlargement of cities, villages, development of economy and raising of cultural inquiries of the population the consumption of water increases with each year. While choosing a water source for water supply its output and quality of water, and, also stability of parameters, which characterize its reliability that is determined by its origin and conditions of formation of water quality, and also character and intensity of its pollution are taken into consideration

The pollution of water sources represents the important ecological problem. Depending on type of pollution there are: chemical, physical (radioactive substances, hot water), bacterial, virus and biological. Industrial wastewater is characterized by considerable quantity of components.

It is a lot of chemical substances, which come at reservoir, worsen biological and organoleptic properties of water (smell, smack, color, turbidity, formation of a pellicle, foams etc) that not favorably influences on water usage and population’s health. 

The output of industries, agriculture, and urban commu­nities generally exceeds the biologic capacities of aquatic systems, causing waters to become choked with an excess of organic substances and organisms to be poisoned by toxic materials. When organic matter exceeds the capacity of those microorganisms in water that break it down and recycle it. the excess of nutrients in such matter encourages rapid growth, or blooms, of algae. When they die, the remains of the dead algae add further to the organic wastes already in the water; eventually, the water becomes deficient in oxygen. Anaerobic organisms (those that do not require oxygen to live) then attack the organic wastes, releasing gases such as methane and hydrogen sulfide. which are harmful to the oxygen-requiring (aerobic) forms of life. The result is a foul-smelling, waste-filled body of water, a situation that has already occurred in such places as Lake Erie and the Baltic Sea and is a growing prob­lem in freshwater lakes of Europeand North America. The process by which a lake or any other body of water changes from a clean, clear condition—with a relatively low concentration of dissolved nutrients and a balanced aquatic community to a nutrient-rich, algae-filled body and thence to an oxygen-deficient, waste-filled condition is known as accelerated eutrophication.

SOURCES OF WATER.

 As a matter of fact all water is primarily derived from oceans. In tropical regions, evaporation of water into air is so great that it has been estimated that about 700 gallons (3182.20 litres) of water is evaporated every minute from each square mile (2.59 square kilometres) of ocean surface.

Water reaches earth in the form of rain, hail, snow, dew or mist, from water vapour in the atmosphere, derived mainly from evaporation of the sea, from lakes, rivers and other waters of the land. Sea water contains sodium chloride and land water contains lot of dissolved and suspended impurities, but it evaporates in the form of pure distilled water which reaches earth again in the form of rain, snow or hail. This condensed water from the air, which is the ultimate source of all our natural water supply, is pure except for a few impurities that are absorbed from the atmosphere.

A part of rain water on reaching earth is evaporated again into the atmosphere and a part of it percolates into the earth. Some part of it gets col­lected in the form of lakes, ponds etc. But a major portion of it runs away at once in the direction of natural slope of ground and gets collected in the form of small streams, which forms rivers and finally it runs again to the sea and thus the cycle goes on repeating. This phenomenon is known asHydrolog-cal Cycle.

Sources of Water Supply.

The chief sources of water supply are:

(a)Rain water or snow water,

(b)Surface water i.e., streams, canals, rivers, lakes, tanks and ponds.

(c)Upland surface water and natural/artificial lakes.

(d)Ground water, i.e., wells and springs.

(e)Sea water.

Ground Water. It is superior to surface water, because the ground provides water an effective filtering medium. Water gets filtered and purified, while passing through it. Wells and springs constitute important sources of ground water.

Wells. These are artificial holes or pits dug into the earth to reach the underground water level. They constitute a very important source of water supply in Indian villages. There are four varieties of wells:

(1) Shallow   Wells   are   those   which   do   not penetrate an impermeable stratum. They simply tap the subsoil water, i.e., ground water lying between the surface and first impermeable stratum. The water of these wells gets pollut zd, cither from surface water or from contamination of subsoil water. Their water is moderately hard.

(2) Deep Wells are those which tap some water bearing layer below the first impermeable stratum. They may pass through one or more impermeable layers. They yield comparatively safer water for drinking purposes than shallow wells on account of efficient filtration, because their water travels a greater distance through the eai ⁽h and also gets bet­ter protection from surface contamination by the impermeable strata above. They yield as a rule,more permanent supplies than shallow wells. The water is usually pure and germ free, but is often hard.

(3)Artesian Wells are a variety of deep wells in which water under great pressure comes out to the surface automatically. To accomplish this, the strata, which the well penetrates, must be cup shaped and the upper level of the ground water tapped between the two impervious strata must be higher than the surface of the earth, where the well lies. Thus in such a case the water shoots up. They are named after Artois province in France where they have been in use for a very long time.

 Norton's Abyssinian Tube Wells are really shallow wells which are bored by simply driving iron pipes 1 1/2" to 2" (3.8 to 5 cm.) in diameter and 20-25 ft. (6.096 to 7.62 metres) deep to tap the ground water. A pump is attached to the pipe to draw the water. Chiefly they were used temporarily in the Abyssinian Campaign. Nowadays these are used where the ground water is not many feet deep below the surface of earth. These wells are of use only when a temporary water supply is required. Since water is drawn out by means of pumps, their water is free from most of the dangers manifested in open wells.

Requirements of a Sanitary Well.

Wells

A well is a hole in the earth from which a fluid is withdrawn. Water wells are the most common type. Oil and natural gas wells are also common. Mining companies also pump steam and hot water down wells to remove salt and sulphur from deep in the ground (Gunning.)

Water Wells

The underground water that flows into wells is called ground water. Most of this water comes from rain that soaks into the ground and slowly moves down to the ground water reservoir, an area of soil and rock saturated with water. The top of this zone is the water table, the level at which water stands in a well that is not being pumped (Taylor.)

In damp places, the water table may lie just below the surface. It is easily reached by digging. A dug well is usually lined with bricks, stone, or porous concrete to keep the sides from caving in. In drier places, the water table may be hundreds of feet or meters down. It may be necessary to drill the well and sink pipes. Power-driven pumps usually draw the water out of deep wells (Berger, Cossi, Taylor.)

In some areas, underground water moving down from the slopes of hills and mountains becomes trapped under watertight layers of clay or shale. Wells drilled through these layers in valleys and plains run into water under pressure. Such wells are called flowing artesian wells (Eliav, Weiss.)

Many people depend on wells for their water supply, especially in rural areas. Underground water is usually pure, because soil makes a good filter. This water generally contains dissolved minerals. A well that taps water with a high mineral content is called a mineral well (Taylor.)

Water wells should be located so that they do not collect poisons or disease germs. A well should be at least100 feet (30 meters) from a cesspool and should never be located so that sewage drains toward it. Water from a well sunk through limestone may be dangerous because water runs through crevices and caves in limestone without being filtered. It is also important that surface water does not drain into a well.

(1) It should be tapped in a good soil and should be at least 50 ft. (15.24 metres) away from any possible source of contamination like a leaking cesspool, insanitary privy etc. The distance between the well and the houses of the users should be kept in view. If the well is situated far away, people may not use the well at all.

(2)The site should be sufficiently high to prevent entrance of water from outside into the well.

(3)It should be a deep well, i.e., sunk below the first impermeable stratum.

(4)It should be properly steined, i.e., built with bricks and lined with cement about 1 inch (2.54 cm.) thick or a watertight casting of concrete or bricks set in cement or having a metal wall, reaching below the water level, below which the joints are open to admit the water to the well. The water should only come from the bottom and not through the surface.

(5)Roots of trees should not be allowed to sprout from the linings of the wall.

(6)The space between the well wall and the lining should be sealed by cement grouting.

(7)It should be properly covered to prevent leaves and dust from blowing into it and also to prevent sparrows and pigeons making their nests in the crevices of the well wall.

(8)Around the top of the well, a parapet wall 3 ft. (0.91 metre) high should be provided, so as to prevent the surface water entering the well. The top of this well should be sloping and not horizontal to discourage people sitting on it for washing clothes thereupon and thus contaminating the well water.

(9)There should be a cemented area at least 6 feet (1.83 metres) with a fall away from the well, so that the surface washings may run away from it and not into it.

(10) It is best that no washing of clothes, utensils and bathing of persons be allowed near a well, as it is not uncommon for a well to get infected by washing clothes, etc., of patients suffering from cholera and other diseases. The best way to avoid this practice is to provide a proper washing and bathing place at a distance from the well to which water can be pumped by means of channels.

(11)All hollows, rat holes, foul tanks, cesspits etc. near the well should be filled up and useless trees and vegetation cut down.

(12)It is best to have a hand-pump or any other mechanical contrivance for drawing up the water in a sanitary manner, which should be discharged by a pipe ending at some distance from the well, so that no water after any possible contamination, can run back to the well. In the absence of any provision — of such a mechanical contrivance, it is desirable that a bucket and a chain for public use should be attached to the well permanently.

Qualities of Well Water. For all intents and purposes it is an excellent water. The bacterial count is very low. It is generally free from pathogenic agents. It is cool and sparkling due to the dissolved carbon dioxide of the ground air.

Cleansing of Well. This is done at the close of hot weather, when the water is at its lowest level. The well must be dewatered.

The sides of the well are scraped and all mud, silt, stones or pieces of bricks, which block the pores of bottom of the well, are removed. Subsequently, the well is treated with a solution of 1 part of freshly prepared

slaked lime to 4 parts of water or bleaching powder, or potassium permanganate solution.

Examination of Wells.

The following points should be borne in mind while examining a well:

(1)Size and depth of the well.

(2)Depth of water in the well.

(3)Nature of soil in which the well is sunk.

(4)Any possible sources of pollution within 200 to 350 ft. (60.96 to 106.68 metres) of the well. Practical aspects are discussed subsequently.

(5)Average quantity of water which is daily drawn out.

(6)The way in which water is disposed off.

(7)Mechanical contrivance, with which water is drawn put, e.g., pump, rope and bucket etc.

(8)Whether there are cracks and fissures on the sides or not.

(9)Whether the mouth of the well is closed or open.

Varieties of Springs.

(1)   Surface Springs or Shallow or Land Springs. These  are  outlets of limited collection of ground water resting on the superficial impervious strata. .They are of intermittent nature, supplying water when the level of subsoil water is high, as during rains, and ceasing to flow in summer season (May-June) and starting again in autumn on commencement of percolation. They are an unsatisfactory source of water supply.

(2)   Deep or Main Springs. They derive their water supply from extensive water bearing strata. The water of these springs is clear, sparkling and is generally  safe,  having been  filtered in  its passage through the earth, and the flow is also constant. The water is often hard. These springs have no surface outlets but issue through a fissure or a crack in the soil.

Ordinarily spring water is pure and less liable to contamination, since there is no mechanical means to draw out the water. It is generally cool and palatable, but is highly charged with carbonic acid gas, which it absorbs from the ground. Moreover, on account of passing under pressure, it dissolves out lime and various other mineral salts contained in the soil through which it passes. Consequently, it gets hard and becomes unsuitable for washing andcooking purposes, although it may be valuable from the medicinal point of view.

(3) Hot or Tliennal Springs. These result from continuance of high internal temperature after a volcanic eruption has ceased. They continue to maintain their heat even for centuries. These springs may arise in places even hundreds of miles away from the actual volcanic vent. As examples   may   be   mentioned   springs   ofSitakoond (in Chittagong), Rajgir (in Bihar) Vajreswari (50 miles, i.e. 80.47 kilometres from Bombay) in India, springs of Bath and Buxton in England, and Yellowstone Park in U.S.A.

(4) Mineral Springs. The water of mineral springs is highly charged with minerafsalts and so used for medicinal or therapeutic purposes. There are also Sulphur Springs which contain sulphuretted hydrogen and various sulphides in solution. Water containing iron or magnesium in solution is known as Chalaybeate or Magnesia Water.

Yield of a Spring. It can be determined by:

(1)    Finding out the time, which it takes to fill a vessel of known capacity. The output of water in one hour can thus be determined.

(2)    By leading the entire flow of spring over a V or a rectangular notch and measuring the depth of flow over the side of notch. The yield of a spring can be calculated from charts and different formulae.

Safeguards against Pollution of Springs.

 The sources of pollution such as leaking cesspits, insanitary privies, latrines and stables etc., should not besituated near the springs. The springs should be protected by a masonry structure, which should extend deep into the ground to protect against surface contamination.

(e) Sea Water.

       Distilled sea water is used for drink­ing purposes, on board ships and in places like Aden, where wells happen to be brackish and rain does not fall even for several years. Dis­tilled water is flat to taste as all gases are drivenout of it by boiling and it is consequently un­palatable. So aeration of water should be done by allowing it to trickle down through a long column of wood charcoal, if it is required for drinking purposes. As sea water acts on lead, copper, zinc and iron, none of these metals should be exposed to its action in the condensing apparatus. Silver and tin linings are the best choice for pipes and vessels used for making distillation apparatus.

Hygienic standards of drinking water quality

Sampling of water

                   For physical and chemical examination, about 2 litres water is essential. It must be collected in a clean glass stoppered bottle made of neutral glass. Before collecting the sample rinse the bottle well three times with the water filling it each time, about 1/3 full. For bacteriological examination about 300 ml water is required. It must be collected in clean sterilized bottle made of neutral glass, provided with a ground glass stopper having an overlapping rim. If the water to be sampled contains or is likely to contain chlorine, a small quantity of sodium thiosulphate  is added to bottle before sterilization.

A.      Sampling from Tap

                   If sample is taken from a tap in regular use, the tap should be opened fully and the water run to waste at least for 2 minutes in order to flush the stagnant water in nozzle and pipe. If sample is taken from tap not in regular use, the tap should be sterilized by heating it till it is red hot. Then allow water to run to waste for one minute and then collect sample.

B.      Sampling from a well:

                   Tie a sample bottle with a rope. Use a stone or piece of metal weighing about 500 gm as "the weight and attach the tube bottle just above it. After removing the cap aseptically, lower the bottle into the well into the well to a depth of 1m. When no more air bubbles rise to the surface, raise the bottle out of the well and carefully replace the cap.

C.      Sampling from stream.

                   Water is taken from middle of a stream, with the mouth of the bottle facing upstream, lower the bottle into the stream and allow filling. Tilt bottle upwards to fill completely. The cap is carefully screwed back, taking care not to touch the screw thread at the top of the bottle.

After taking sample following information must be given with bottle.

a.       Source of water supply

b.      Date, place and time of sampling

c.       Geological formation of soil, if available.

d.      In case of well, its depth, diameter and how it is used.

e.       Recent rainfall if there.

f.       Any suspected source of pollution in vicinity

g.       Whether any method of purification is used.

PURIFICATION OF WATER

Three main steps in purification of water on large scale:

Storage, Filtration, Chlorination

1. Storage:

Water is drawn out from source and impounded in natural or artificial reservoirs. Storage provides a reserve of water from which further pollution is excluded.

Advantages
a.       Physical — About 90% of suspended impurities settle down in 24 hours by gravity.

b        Chemical — The aerobic bacteria oxidize the organic matter present in water with the aid of dissolved oxygen. As a result the content of free ammonia is reduced and a rise in nitrates occur.

c.       Biological — 90% of total bacterial count drops in first 5 - 7 days.

2. Filtration

Filtration is important because 98 - 99% of bacteria are removed by filtration, a part from other impurities. Two types of filters are in use, they are:

a.       Slow sand filters (biological filters)

b.       Rapid sand filters (Mechanical filters)

a. Slow Sand Filter.  

ADVANTAGES OF filter.doc

Following are the elements of a slow sand filter.

*        Supernatant (raw) water:

Supernatant water is present above sand bed, its depth varies from (1 – 1,5 m). It serves 2 important functions.

i.        It serves as a constant supply of water,

ii.       It provides waiting period of some hours and there is partial purification by sedimentation & oxidation

*        Sand bed:

It is most important part of the filter; its thickness is about (1,2 m). The sand grains are of diameter between (0,15 – 0,35 mm). Sand bed is supported by a layer of graded gravel. Water percolates through the sand bed very slowly and during this it is subjected to number of purification processes — mechanical straining, sedimentation, adsorption, oxidation and bacterial action.

Vital Layer

Few days (3 to 5 days) after laying the filter, surface of sand bed gets covered with a slimy, green coloured growth made of fungi, algae, bacteria, diatoms and plankton. The formation of vital is known as "ripening of the filter". The growth present on sand bed is called as "Schmutzdecke". It removes organic matter, holds bacteria and oxidizes ammoniacal nitrogen into nitrates and helps in yielding a bacteria - free water.

 Under - drainage system

It consists of porous or perforated pipes lying at the bottom of the filter bed and provides an outlet for filtered water and also provides support to the filter medium above.

Slow filters clear water well only after they’re "ripening": the diameter of pores in the sand decreases, owing to the keeping of suspended matters in the highest layer. So, small particles, worm eggs and larvae and to 99.9% of bacteria can be detained. The clean sand does not absorb viruses. But after the "ripening", about 50-99% viruses are kept in the slow filters. If such filters are used correctly they free water from cercaria. At the same time the series of biological processes proceed in the ripped highest layer - biological film: the mineralization of organic matters and the death of bacteria. The contaminated highest layer of the sand is changed in 30-60 days.Slow filters are used when water turbidity doesn't exceed 200 mg/l in the small country water-pipes. They are always used after the preceding aeration to remove surplus iron and manganese.

Filter control valves:

The filter is equipped with certain valves and devices which are incorporated in the outlet pipe system maintaining a steady rate of filtration.

When the vital layer becomes dense and resistance to the passage of water is increased the supernatant water is drained off Sand bed is cleaned by scrapping of the top portion of the sand layer to a depth of 1 - 2 cms. Scrapping is done 20 - 30 times. The process is known as Filter Cleaning.

b. Rapid Sand Filter

Rapid sand filters are of two types, the gravity type and the pressure type. Both the types are in use. The following steps are involved in the purification of water by rapid sand filters.

 i. Coagulation:

Raw water is treated with a chemical coagulant such as alum. The dose required is usually 5 - 40 mg/liter.

ii. Rapid mixing:

The treated water is subjected to rapid mixing for few minutes. This allows a quick and thorough dissemination of alum throughout the bulk of water.

iii. Flocculation:

Treated water is gently stirred in a "flocculation chamber" for about 30 minutes. In chamber there are paddles which act as flocculator. They rotate at speed of 2 to 4 rate per minute. This slow and gentle stirring results in the formation of a thick, copious, white flocculent precipitate of aluminum hydroxide. The thicker the precipitate or flock diameter, the greater the settling velocity.

iv. Sedimentation:  •

The coagulated water is now led into sedimentation tanks where it is detained for periods varying from 2 - 6 hours.

v. Filtration:

The partly clarified water now subjected to rapid and filtration.

 Filter Beds:

Each unit of filter bed has a surface of about 80 - 90 m². Sand is filtering medium. The effective size of sand particles is between 0.6 - 2.0 mm. The depth of sand bed is usually about 1 m.  Below the sand bed is a layer of graded gravel 30 - 40 cm. The gravel supports the sand bed and the filtered water to move freely towards the under drains. The rate of filtration is 5 - 15 m³/ m²/hour.

Back - Washing:

Rapid sand filters need frequent washing daily or weekly. Washing is accomplished by reversing the flow of water through the sand bed, which is called "back-washing". Back - washing dislodges the impurities and cleans up the sand bed.

The disinfection is one of the most usable methods of water improvement. Usually it is a concluding and very important stage. The most spread methods of disinfection are different methods of chlorination. Sometimes ozonization and UV-irradiation use also.

3. CHLORINATION

Chlorination is the process in  which chlorine is added to water for purification. Chlorination-is more effective when pH of water is around 7.

 Effects of Chlorine:

a.       Chlorine kills pathogenic bacteria, it has no effect on spores and certain viruses.

b.       It has germicidal effects.

c.       It oxidizes iron, manganese and Hydrogen sulphide

d.       If destroys some taste and odour producing constituents.

e.       It controls algae and slim organisms

f.        It aids coagulation

Action of Chlorine.

When Chlorine is added to water, there is formation of hypochlorous and hydrochloric acid. The hydrochloric acid is neutralised by alkalinity of the water. The hypochlorous acid ionizes to form hydrogen ions and hypochlorite ions as follows.

H₂O + CI₂     ►      HCI^--+HOCI

HOCI            ►         H⁺⁺OCI"

The disinfecting action of-chlorine is mainly due to hypochlorous acid and to a small extent due to hypochloriteon.

The chlorination of water is one of the most spread methods and it is of great importance for the prophylaxis of water epidemics. It is explained by the reliable disinfection, accessability and cheapness.

The principle of chlorination is based on the treatment by chlorine or the chemical compounds, containing active chlorine and able to oxidize and provoke bactericidal action. Chlorine is subjected to hydrolysis in water:

Cl₂+HOH → HOCl+HCl, so hydrochloric and chloricious acids are formed. Chloricious acid takes the central place in the mechanisms of bactericidal action. It was thought earlier that the latter was destroyed in water and discharged out atomic oxygen (HOCl → HCl+O·), which was the main bactericidal agent. Now, such explaination is considered insufficient. Chlorine in the structure of chloricious acid and hypochlorite-ion (HOCl→H +OCl ) free active chlorine, which determines bactericidal action in water. Not large molecules and electric neutrality let chloricious acid penetrate quickly through the bacterial membrane and influence upon the cellular enzymes, important for the metabolism and reproduction. It is assumed, that it reacts with SH-groups of enzymes, which become oxidized.

The reliable bactericidal effect of chlorine is achieved, if about 0,3 – 0,5 mg/l of free chlorine or 0,8 – 1,2 mg/l of connected chlorine are left in water after 30 - 60 min. of exposure.

Sanitary control of water pipes includes the determination of the remaining chlorine in water every hour, and the bacteriological investigation - not rare than once a day. Long-term experience of using such method in almost all countries of the world is evidence of chlorinated water safety for use.

Simple chlorination (by chlorine request). Right choice of the dose is of great importance for the reliable disinfection. Only about 1 – 2 % active chlorine are spent on the bactericidal action during the disinfection. The rest part is spent on oxidation of organic and inorganic matters in water. All these connected forms of chlorine form such a notion as "chlorine-absorbability of water". Different natural waters have different chlorine-absorbability. To disinfect water by such a method, they introduce such amount of chlorine, that the remaining free chlorine should be 0,3 - 0,5 mg/l and the remaining chlorammoniac chlorine – 0,8 - 1,0 mg/l. In such a case the organoleptic features of water do not become worse.

The number of active chlorine (mg), necessary for the disinfection of 1 liter of water, is called chlorine’s need of water (chlorine-request). It is determined by the experimental chlorination of certain volume of water, subjected to disinfection.

Besides the correct dose, good mixture and sufficient contact of chlorine with water are necessary for the effective disinfection.

The presence of suspended matters, gumines and other organic compounds in water lowers the action of chlorine. That's why it is necessary to light and decolourize turbid and colored waters before disinfection.

The chlorination of water by chlorine-request reliably disinfects water from the intestinal infections (typhoid fever, dysentery, cholera, patogenous strains of E.coli, salmonellas), brucellosis, tularemia, leptospirosis. There are some disputes about the polio virus. Many scientists consider, that this virus is inactivated by the chlorination for an hour. Water, containing Berket's rikketsia, amoebic cysts, worm eggs and the spores of some types of anthrax, cannot be disinfected by this method.

At chlorination of water under action of active chlorine oxidize the microorganisms, organic and inorganic substances, which are in water; the part of chlorine is absorbed by the substances, which have hanged in water, that is denoted as the chlorine absorption of water.

For reliable decontamination of water its contact with chlorine must be last: in summer - not less than 30 minutes, and in winter - not less than 1 hour. The residual chlorine (chlorine, which has remained in water after its decontamination) is the criterion of complete satisfaction of the chlorine absorption of water and also of the epidemic safety of water. Water which was correctly chlorinated must contain 0,3-0,5 mg/l of residual chlorine, as water, which contains more than 0,5 mg/l of residual chlorine, has specific unpleasant taste and smell. The sum of the chlorine absorption of water and the quantity of residual chlorine (0,3-0,5 mg/l) makes the chlorine’s need of water for chlorinate.

The chlorination by the post-break doses. By the results of some investigations the water can be disinfected by 2 doses of chlorine: 1mg/l (before-break dose) and 5,2 mg/l (post-break doses), as the concentration of the rest chlorine makes 0,5 mg/l in both cases.

However, by before-break dose the remaining chlorine is determined as chloramin, and by post-break doses - as free chlorine. The bactericidal action of such method is very effective. At the same time we improve water organoleptic features at the expense of oxidation of organic substances with the bad smell. It is necessary to use this method in hot countries widely.

The chlorination with the preammonization (chlorammination).

First, they introduse ammoniac solution and than, in 0.5-1 min, chlorine to the water. As a result chloramins are formed in water: NH₂Cl - monochloramin and NHCl₂ - dichloramin. The last one has the most expressed bactericidal action. The effectiveness of such method depends on the ratio NH₃:Cl. That's why they use the doses of reagents in the following ratios: 1:3, 1:4, 1:6, 1:8. The ratio should be chosen for certain reservoirs individually.

This method prevents bad smells, which can appear by the chlorination of water, containing phenol and the matters from its group (as chlorphenols are formed). Chlorphenols impart medicinal smell and smack to the water even in the small quantities.

The speed of disinfection by this method is lower than that by chlorine. The exposure time should be not less than 2 hours.

If the water of reservoirs contains ammonium salts, chloramines are also formed. This fact decelerates disinfection. So, it is necessary to define free and connected chlorine separately to determine the reliability of disinfection. Obviously, the presence of only free chlorine is evidence of reliable disinfection.

Double chlorination. In many river water-pipes chlorine is given before the settling and than after the filtration as usual. The introduction of chlorine before the settling improves the coagulation and decolorization of water, inhibits the development of microorganisms in the settling tanks, increases the reliability of disinfection. However, the possibility of chlororganic compounds formation increases too.

The ozonization of water. It is widespread in the industrial countries. Ozone is destroyed in water, forming atomic oxygen: O₃ → O₂  → O. Now, it is proved, that this mechanism is more complicated: there are many intermediate reactions with the formation of free radicals (for example, HO₂), which also have oxidizing features. Ozone oxidizing potential (+1.9) is higher than that one of chlorine (+1.36). From the hygienic point of view, ozonization is one of the best methods of disinfection: water is well disinfected, organic admixtures become destroyed, organoleptic features are improved. Water becomes blue and it is equated with spring water.

Ozone dose is 0,5 - 6 mg/l. Sometimes, higher doses are necessary for the lighting of water and improving other organoleptic features. The time of disinfection is 3-5 min. The remaining ozone should make up 0,1 – 0,3 mg/l. The concentration of the remaining ozone 0.4 mg/l provides the reliable inactivation of 99 % viruses for 5 min.

UV-irradiation.

The maximal bactericidal effect is achieved by the waves 250-260 nm, which pass even through the 25 cmlayer of transparent and decolorized water.

The disinfection proceeds very quickly: vegetative forms of microorganisms die in 1-2 min. The turbidity, colour and iron salts decelerate the disinfection, decreasing the transparence of water. Consequently, it is necessary to light and decolorize water before the disinfection.

There are some advantages of UV-irradiation over the chlorination: bactericidal rays don't denaturate the water and don't change its organoleptic features, they have wider biological action. Their bactericidal action is spread over the spores, viruses and worm eggs, resistant to chlorine. Many investigators consider this method the best for the disinfection.

PURIFICATION OF WATER ON SMALL SCALE

The boiling.

It is the simplest method of disinfection. Vegetative forms of pathogenous microorganisms die in 20-40 sec. at the temperature -  80 °C. The water is almost disinfected until it begins to boil. 5 minutes of boiling provides reliable safety even in the very strong pollution by suspended matters, viruses and other pathological agents. During 30 min. of boiling most of spores die too. The spores of anthrax, worm eggs and larvae are inactivated. Protozoa die too. This method is often used in the everyday life, in hospitals, child welfare institutions, in the manufactures, railway stations. It is necessary to clean tanks before filling them with the boiled water and change water every day, as the microorganisms multiply here very quickly.

Chemical tablet methods. The use of tablets and solutions are widely used for the disinfection in the expeditions and hikes. Tablets "Halazone" contain chloramin, stable during the storage. The tablet is introduced to a certain volume of water (usually it is 1 liter), water and stirred every 3-5 min. It can be used in 30 min. But this tablet cannot be enough for the very contaminated water.

In these cases we can use tablets "Chlor-dechlor", which contain more chlorine and dechlorinated agent in the middle of the tablet (sodium hyposulphite). They introduce one tablet to the water and stir it every 2-3 min. thoroughly. After dissolving of the external part of the tablet its central part inactivates the surplus chlorine. If the water is very shady introduce 2-3 tablets at once. In Ukraine, we use tablets "Aquasept" and "Aquacide", which contain steady chlorine-containing preparations. One tablet (3,5 mg of active chlorine) is introduced to the 1 liter of water. Water becomes desinfected in 30 min.

Iodine-containing preparations are widespread in tropical countries. They disinfect water from bacteria, many viruses and cysts. The simplest method is the disinfection by 10 % solution of iodine: 2 drops of such solution are introduced in 1 liter of very contaminated water. The water is usable in 20-30 min. Tablets "Globaline", "Potable", containing sodium tetraglycerate triiodate, disinfect water from bacteria, amoebic cysts, many viruses. They are the best disinfectant matters for the torrid zinc. They are safe for humans. Large tanks for the preservation of water must have sturdy cover and a tap.

EXPRESS METHODS OF WATER QUALITY IMPROVING.

Deodorization - elimination of smack and odour of water by aeration, usage of oxidants (ozonization, dioxide of chlorine, large doses of chlorine, potassium permanganate), filtrating through a layer of absorbent coal, by introduction in water to sedimentation of absorbent coal.

Deironation is carried out by spraying water with the purpose of aeration in graduation towers. Thus, bivalent iron is oxydated in ferric hydroxide, which sediments in settling tank, or delays on the filter.

Softening. By an aged method of water softening is soda calcareous, at which calcium and magnesium settle in a settling tank as unsolvable salts. Today is used filtrating water through filters, which are completed by ion exchangers. Ion exchangers are firm, unsolvable, acinose stuffs, which have property to exchange their ions on ions of salts, which are solved in water.

Desalting - the sequential filtrating of water through kationite, and then through anion exchanger permits to liberate it from solvable salts and consequently use with the purpose of desalting. For desalting water on water pipes, sea courts thermal method is used which bases on evaporation of water with the following condensation of steams. Also is used electro dialysis with usage of selective diaphragms, freezing and other methods.

Decontamination - at coagulation, settling and filtrating of water on waterpipes contents of radioactive substances in it is reduced only on 70-80%. For more penetrating decontamination water is filtrated through ionic exchanger of resin.

Fluoridation of water - synthetic adding of fluorine bonds with the purpose of decrease of its rate by caries of teeth.

The protective effect of fluoride occurs primarily during infancy and early childhood when the teeth are developing, but its caries-preventive action is carried over into adulthood as long as one has access to fluoridated water.

WATER PURIFICATION

Suspended and dissolved impurities present in naturally occurring water make it unsuitable for many purposes. Objectionable organic and inorganic materials are removed by such methods as screening and sedimentation to eliminate suspended materials; treatment with such compounds as activated carbon to remove tastes and odors; filtration; and chlorination or irradiation to kill infective microorganisms.

In aeration, or the saturation of water with air, water is brought into contact with air in such a manner as to produce maximum diffusion, usually by spraying water into the air in fountains. Aeration removes odors and taste caused by decomposing organic matter, and also industrial wastes such as phenols and volatile gases such as chlorine. It also converts dissolved iron and manganese compounds into insoluble hydrated oxides of the metals, which may then be readily settled out.

Hardness of natural waters is caused largely by calcium and magnesium salts and to a small extent by iron, aluminum, and other metals. Hardness resulting from the bicarbonates and carbonates of calcium and magnesium is called temporary hardness and can be removed by boiling, which also sterilizes the water. The residual hardness is known as noncarbonate, or permanent, hardness. The methods of softening noncarbonate hardness include the addition of sodium carbonate and lime and filtration through natural or artificial zeolites, which absorb the hardness-producing metallic ions and release sodium ions to the water. Sequestering agents in detergents serve to inactivate the substances that make water hard.

Iron, which causes an unpleasant taste in drinking water, may be removed by aeration and sedimentation or by passing the water through iron-removing zeolite filters, or the iron may be stabilized by addition of such salts as polyphosphates. For use in laboratory applications, water is either distilled or demineralized by passing it through ion-absorbing compounds.

WATER DESALINIZATION

Water Desalinization Technique Flash evaporation is the most widely used method of water desalinization. The seawater is heated and then pumped into a low-pressure tank, where the water is partially vaporized. The water vapor is then condensed and removed as pure water. This process is repeated many times (three stages are shown). The remaining liquid, called brine, contains a large amount of salt and is removed and often processed for minerals. Note that the incoming seawater is used to cool the condensers in each evaporator. This design conserves energy since the heat released when the vapor condenses is used to heat the next batch of seawater. 

         To meet the ever-increasing demands for fresh water, especially in arid and semiarid areas, much research has gone into finding efficient methods of removing salt from seawater and brackish waters. Several processes are being developed to produce fresh water cheaply.

Three of the processes involve evaporation followed by condensation of the resultant steam and are known as multiple-effect evaporation, vapor-compression distillation, and flash evaporation. The last-named method, the most widely used, involves heating seawater and pumping it into lower-pressure tanks, where the water abruptly vaporizes (flashes) into steam. The steam then condenses and is drawn off as pure water.

Freezing is an alternate method, based on the different freezing points of fresh and salt water. The ice crystals are separated from the brine, washed free of salt, and melted into fresh water. In another process, called reverse osmosis, pressure is used to force fresh water through a thin membrane that does not allow the minerals to pass. Reverse osmosis is still undergoing intensive development. Electrodialysis is being used to desalt brackish waters. When salt dissolves in water, it splits into positive and negative ions, which are then removed by electric current through anion and cation membranes, thus depleting the salt in the product water. Although developmental work on electrodialysis is continuing, a number of commercial plants are in operation.

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COAGULATION

The coagulation is used to accelerate the sedimentation of suspended matters, filtration and lightening of water. They add the following coagulators to water: Al₂(SO₄)₃, FeCl₃, FeSO₄ and so on. They form unsoluble compounds with the dissolved electrolytes, which are quickly sedimented as flocks. These flocks have a large active surface and positive electric charge. That's why they absorb even the smallest negative microbe particles and colloidal gumines, taking them to the bottom of the settling tank. The transparent and uncolored filtrate is formed after the sedimentation of flocks and the next filtration of water. The use of coagulators allows decolorizing water, to shorten the time of settling to 2-3 hours and to use fast filters. 95% worm eggs, 90% and more bacteria and viruses are left water after the coagulation and settling. Coagulation belongs to the most effective methods of water clearing from viruses. The best cleaning is realized by the combined coagulator (Al₂(SO₄)₃ and iron salts).

Aluminium sulpfate Al₂(SO₄)₃*18H₂O is often used as a coagulator. It reacts with the calcium bicarbonate and forms Al(OH)₃, which is bad-dissoluble and sediments as flocks. The dose of coagulators is 30-200mg/l, it depends on the color, turbidity, pH of water and many other conditions. It is determined by the experi ment for the certain water. Lately they have been used large-molecular matters - flocculators (activated silicic acid), which are active in very small doses (0,2 – 2,0 mg/l), to accelerate coagulation and economize the coagulator. 5% solution of coagulator is given to the mixer with the help of special dosator, where it is quickly mixed with water. Then, the water enters the reaction chamber, where the formation of flocks completes in 10-20 min. Such water passes to the settling tank, where the flocks are sedimented. The size of settling tank corresponds to the settling for 2 – 3 hours.

Then the water is given to the fast filters, where the layer of sand is 0,8 – 1,2 m and the granules - from 0,5 -1 mm. The speed of filtration is 5 - 8 m/h (it is automatically regulated). Soon after the beginning of the work, the filtrating film, consisting of the flocks of coagulator and unsedimented particles, is formed in the highest layer. It improves the detain of microorganisms and admixtures. In 8-12 hours the film becomes denser and the speed of filtration decreases. That's why the work is stopped and the filter is cleaned for 10-15 min. by the stream of clean water, directed upwards, to remove the film.

HYGIENE OF SOIL AND CLEANING INHABITED PLACES