The lecture Water Hygiene and Hygiene of water-supply of inhabited places Author: Lototska O.V. Water is a chemical substance. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often coexists on Earth with its solid state, ice, and gaseous state (water vapor or steam). •Water covers 71% of the Earth's surface; the oceans contain 97.2% of the Earth's water. Every organism consists mostly of water. The human body is usually made up of 50 to 75 percent water. All living things need a lot of water to carry out their life processes. Functions of Water in the Human Body Water is essential for digesting food. It is also important for getting rid of various toxic elements from the body, in the form of urine, sweat and fecal matter. Water helps to cushion our joints and prevents shocks in them. Water present in blood is the carrier of oxygen and nutrients to all our body cells. Water present in lymph (a fluid that is part of our immune system) helps the body to fight against various diseases. Water helps to regulate and maintain our body temperature. That explains why wet poultices are used to cure fevers. Water prevents dehydration and thus, helps to maintain proper metabolism in our body. Uses of water Domestic Use: 7 % of water available is for domestic use i.e drinking, cooking, washing, bathing etc. Recommended need of water is 120 liters/day/person. It includes all aspects of life which a person has in his routine life i.e bathing, washing, drinking & for toilet use. Public purpose: Water is required for public cleansing, maintenance of gardens, and swimming pools and other civic activities. Industrial Use: 23 % of available water is used in industries. Agricultural Use: 70 % of available water is used for growth of food and raw materials required. Epidemic and toxicological significance 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 malarial haemamoeba and others (open water reservoirs). 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. Chronic (long term) exposure to Fluoride in water above 1.5 - 2 mg/liter can result in coloration of the teeth (fluorosis). At higher levels, more severe impacts can result including alteration of bone density resulting in arthritis and tooth damage. Mild fluorosis looks like this: 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; - 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; - watering of the green areas within settlements; 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. Sources of water Sources where water may be obtained include: •Ground water •precipitation which includes rain, hail, snow, fog, etc. •surface water such as rivers, streams, glaciers RAIN Prime source of all water. Part of rain water sinks to form ground water, part of it evaporates and some runs in streams and rivers. These events are called "water - cycle". Characteristics: Purest, bright & sparkling colour, soft water, only traces of dissolved solids, corrosive action on lead due to softness, in clean areas rain water is free of pathogens. Impurities: Picks up local impurities such as dust, soot, micro-organisms, CO2, N2, O2, Ammonia & Sulphur. In areas where NO2 and SO2 are present in atmosphere, rain water becomes acidic and the rain is called acidic rain. SURFACE WATER Surface water mostly originates from rain water. It has highest chance of being polluted particularly river water because people near banks throw wastes in it. Sources of surface water are. a. Impounding reservoirs b. Rivers and streams c. Tanks, ponds and lakes. GROUND WATER It is in form of: a. Wells — Deep well, shallow well, Artesian well. b. Springs — Seasonal springs, thermal springs, mineral spring, shallow springs, and deep springs. a. b. c. a. b. The advantages of ground water are: It is usually free from pathogenic agents. It usually requires no treatment. Its supply is continuous. The disadvantages of ground water are: It is high in mineral contents It requires pumping or some arrangement to lift the water. Springs: A spring is ground water which finds its way to the surface because of topographical features. Cracks present in earth, water enters and comes out from other opening at a low level. So source may be quite far away such as 100-200 miles. 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 villages. There are four varieties of wells: There are four varieties of wells: 1. Shallow Wells, 2. Deep Wells 3. Artesian Wells are a variety of deep wells in which water under great pressure comes out to the surface automatically 4. Tube wells, popularly known as Norton's Abyssinian Tube Wells are really shallow wells which are bored by simply driving iron pipes 3.8 to 5 cm in diameter and 6 to 7.62 metres deep to tap the ground water. A pump is attached to the pipe to draw the water. Types of aquifers and wells. In a water table well, the water table is at atmospheric pressure. In an artesian well, the water pressure is greater than atmospheric. In a flowing artesian well, the water pressure is such that it can flow freely above the ground surface The population should be provided not only with enough of water, but also with qualitative water. Water should not cause any pathological change in the organism, should not cause of spread of infectious diseases, and also not to cause unpleasant sensations. Waters, used for drink and everyday needs, must correspond to the demands: good organoleptic properties: refreshing temperature, transparence, colorless, no smell and no taste . harmlessness of its chemical composition the absence of pathogenic microorganisms safety in the radiological attitude 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. Major categories of water pollutant 1. Infections agents - Bacteria, viruses 2. Organic chemical - Pesticides, plastics, detergents, oil, and gasoline 3. Inorganic chemicals - Acids, caustics, salts, metals 4. Radioactive materials - Uranium, thorium, cesium, iodine, radon Hazards of Polluted Water: 1. Biological Hazards These are due to some specific agent that causes illhealth. Bacterial Viral Protozoal Typhoid, Bacillary dysentery, Cholera etc. Viral hepatitis A & E, Poliomyelitis. Amoebiasis, Giardiasis. Leptospiral Round worm, whip worm, hydatid disease Weil's disease Cyclops Guinea worm. Helminthic 2. Other Hazards a. GIT disturbances due to Na ++, Mg ++ & Ca++ ions, e.g) increased MgSO4 lead to diarrhea. b. Lead poisoning c. Iodine deficiency d. Fluorine deficiency e. Hardness of water f. Infant methaemoglobinemia. Impure water may be purified by either of the following methods: A. Natural (a) Pounding or Storage. (b) Oxidation and Settlement. B. Artificial I. Physical Distillation. Boiling. II. Chemical Precipitation. Disinfection or Sterilization. III. Filtration "Biological" or "Slow Sand" Filtration. "Rapid Sand" or "Mechanical" Filtration. Domestic Filtration. PURIFICATION OF WATER Purification of water is of great importance in community medicine. It may be considered under two headings. Purification of water on large scale Purification of water on small scale 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 Physical — About 90% of suspended impurities settle down in 24 hours by gravity. 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. 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) Slow sand filter Supernatant (raw) water: Sand bed Vital Layer Under drainage system 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. Filter Beds: 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 following steps are involved in the purification of water by rapid sand filters. i. Coagulation: ii. Rapid mixing: iii. Flocculation: iv. Sedimentation: v. Filtration: How is water treated? Coagulation: Alum and other chemicals are added to water to form tiny sticky particles called "floc" which attract the dirt particles. Sedimentation: The heavy particles (floc) settle to the bottom and clear water moves to filtration. Filtration: The water passes through filters that help to remove smaller particles. Disinfection: A small amount of chlorine is added to kill any bacteria or microorganisms that may be in the water. Storage: Water is placed in a closed tank or reservoir where it flows through pipes to homes and businesses in the community. 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 HOCI ► ► HCI- + HOCI H+ + OCI- The disinfecting action ofchlorine is mainly due to hypochlorous acid and to a small extent due to hypochloriteon. Principles of Chlorination a. First, water should be clear and free from turbidity. b. Chlorine demand of water should be estimated. c. At least one hour is essential as a contact period of free residual chlorine for killing bacterial and viruses. d. Minimum recommended concentration of free chlorine is 0.5 mg/L for one hour. e. The sum of the chlorine demand of the specific water plus the free residual chlorine of 0.5 mg/l constitutes the correct dose of chlorine to be applied. Agents alternative to Chlorination The ozonization of water Ozone contains three oxygen atoms. It is destroyed in water, forming atomic oxygen: O3 → O2 → O. 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. Asaka Water Purification Plant Ozone has been used in water treatment since 1903. It is more effective against bacteria and viruses than chlorine and adds no chemicals to the water. Ozone cannot be stored and requires an on-site ozone generator. In general, ozonation equipment and operating costs are higher than other treatment procedures Advanced Water Purification System Ultraviolet Light Ultraviolet irradiation will kill bacteria by creating photochemical changes in its DNA. No chemicals are added to the water by this process. Most ultraviolet water treatment units consist of one or more ultraviolet lamps usually enclosed in a quartz sleeve, around which the water flows. The UV lamps are similar to fluorescent lamps and the quartz sleeve surrounding each lamp protects the lamp from the cooling action of water. The killing effect of the lamp is reduced when the lamp temperature is lowered. Ground water is usually a constant temperature year round and so it is possible to set a flow rate that will not lead to excess cooling. The effectiveness of UV irradiation depends on • the intensity of the light, • depth of exposure and • contact time. Water passes in a relatively thin layer around the lamp; therefore, water flow must be regulated to ensure that all organisms receive adequate exposure. If the water is at all turbid, or if it contains traces of iron, the effectiveness of UV is greatly reduced. In such cases, the water needs to be filtered before it reaches the UV system. The maximal bactericidal effect is achieved by the waves 250-260 nm, which pass even through the 25 cm layer 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 irradiation over the chlorination: UV- 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 •House hold purification of water •Disinfection of wells HOUSE HOLD PURIFICATION a. By Boiling: Water should be boiled for 5 -10 minutes. It kills all bacteria, spores, cysts & ova. It removes temporary hardness Taste is altered but is harmless b. Chemical disinfection i) Bleaching Powder (CaOCI2) Bleaching powder is a white amorphous powder. Produced by action of chlorine on slaked lime. When freshly made contains 33 % of available chlorine. It must be stored at dark, cool, dry place in a closed container that is resistant to corrosion. In practise one cup (250 g) of laundry bleach is mixed with three cups (750 ml) of water to make a litre. Three drops of this solution are added to 1 litre water for disinfection. Contact period is 30 minutes to 60 minutes. ii Chlorine Solution Chlorine solution may be prepared from bleaching powder. * If 4 kg of bleaching powder with 25 % available chlorine is mixed with 20 litres of water, it will give a 5% solution of chlorine. * This solution should be kept in dark, cool and dry place in closed container iii. Chlorine tablets Available under different trade name e.g. Halazone One tablet of 0.5 g is sufficient to disinfect 20 litres of water. Used in camps and during travel. iv. Iodine: Two drops of 2 % ethanol solution of iodine is used. A contact period of 20 - 30 minute is sufficient for 1 litre water. v.Potassium Permanganate. It is a powerful oxidizing agent but not recommended as it alters colours, smell and taste of water. 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 iron hydroxide, which sediments in settling tank, or delays on the filter. Softening or Removal of hardness a. b. c. d. a. b. I.Temporary Hardness Boiling Addition of lime Addition of sodium carbonate Permutit process II. Permanent Hardness Addition of sodium carbonate Permutit process/ Base exchange process. Boiling: It removes temporary hardness by expelling carbon dioxide and precipitating the insoluble calcium carbonate. Ca (HCO3)2→ CaCO3 + CO2 + H2O Addition of Lime: It removes temporary hardness. Lime absorbs carbondioxide and precipitates the insoluble calcium carbonate. Ca (OH)2 + Ca (HCO3)2 →2 CaCO3 + 2H2O Addition of Sodium Carbonate, It removes both temporary and permanent hardness. Na2CO3 + Ca (HCO3)2 → 2NaHCO3 + CaCOs Na2CO3 + CaSO4 → Na2SO4 + CaCO3 Base Exchange Method In this method sodium permutit is used, which is a combination complex of Na, Al and Si (Na2 Al2 Si2OH2O) Sodium permutit has property of exchanging the sodium cation for Ca++ and Mg++ ions in water. Na2 Al Si2O + H2O = Mg++/Ca++ When hard water passed, sodium permutit exchanges Mg/ Ca and is converted into calcium and magnesium permutit. With time permutit loses effectiveness, it is regenerated by adding conc. sol of NaCI. * By this process hardness of water is removed to zero. As zero hardness is corrosive, therefore a part of raw water is mixed with softened water. Desalting About 97 percent of the water on earth is in the salty oceans. People have found many ways to desalinate, the process for removing salt from seawater and brackish water. The desalination processes used most commonly today are distillation, reverse osmosis, and electrodialysis. These processes produce fresh water from salt water. This is a water purification plant Distillation is the oldest method of turning salt water into fresh water. Seawater can be distilled by simply boiling it in a teapot, and piping the steam into a cool bottle. The salt water turns to vapour under the sun's heat. The vapour rises until it hits the underside of the dome or glass, where it condenses. Most modern distillation plants use a process called multistage flash distillation. This is a type of the age-old method of boiling and condensation. In flash distillation, preheated seawater flows into a large chamber in which the pressure is low. The low pressure causes some of the water to instantly turn into steam The steam is condensed into salt-free water. The seawater passes through several distillation chambers. Each of the chambers has a lower pressure than the previous chamber. Often, the final water is so pure that it is tasteless, and some salt must be tossed back in to give it flavour Reverse osmosis is a widely used method for desalting seawater and brackish water. In normal osmosis, a less concentrated liquid flows through a membrane into a more concentrated liquid. Thus, if salt water and fresh water are separated in a chamber by a special semi-permeable membrane, the fresh water will flow through the membrane into the salt water. Electrodialysis is used chiefly to desalt brackish ground water and water from estuaries, or river mouths. Electrodialysis is based on the fact that when salt is dissolved in water, it breaks up into ions, or electrically charged particles, of sodium and chloride. Sodium ions carry a positive charge, and chloride ions carry a negative charge. Other desalting processes are also being studied. During the 1970's, several plants experimented with freezing as a method of desalination. When seawater freezes, the ice crystals produced are pure water in solid form. The salt is separated and trapped between the ice crystals. 0,7-1,5 mg/dm3 of fluoride is the optimal concentration of fluoride in water. Fluoridation is addition of fluoride to public water supplies to reduce tooth decay. Fluoride is a compound consisting of the element fluorine and a metallic element such as sodium (forming sodium fluoride, used in water supplies) or tin (forming stannous fluoride, used in toothpaste). Water fluoridation has been recognized as a significant method in preventing tooth decay since the 1930s. The maximum protection by fluoridation against tooth decay occurs when children consume fluoridated water from birth through age 13. For hygienic purposes the examination of water is generally done under the following heads: 1. Physical Examination. 2. Chemical Examination. 3. Microscopical Examination. EXAMINATION OF WATER Before water from any 4. Bacteriological Examination. source is declared fit for human consumption, it is essential to carry out the following examination. Control question: 1. How is water treated? 2. What are the principles of water chlorination ?