Water Supply Schemes
BASICS OF THE WATER SUPPLY SCHEMES
Actually wherever a water supply scheme is framed (scheme means a system to draw water from suitable source, treat it and then supply it to the consumers) a comparison is made between all the possible solutions. Preference is given to the nearest possible source as the conveyance of water is very costly. The underground water is generally pure (from suspended impurities point of view because of natural filtration) but contains more dissolved salts. The lifting of water (pumping out from wells) also requires energy (electricity) whereas the filtration of surface water is a costly affair.
So the environmental engineers in the public health engineering departments (water works) make schemes (plans) to supply potable (fit for drinking from all points of view, i.e. clarity, dissolved salts, and free from bacteria etc.) water to the consumers. The schemes are basically of two types, rural water supply schemes and urban water supply schemes depending upon the population of the habitation. The standards for the two types are different. For example the designed rate of water supply per person per day in rural areas is only 40 litres (except the 11 desert districts of Rajasthan where it is 70 L.P.C.D. including the cattle water demand). The designed rate of water supply for urban area is minimum 135 L.P.C.D. and above for industrial and commercial demands depending upon the population of the city. Similarly, the availability of electricity in rural area is assumed as 8 hours per day whereas it is 20-22 hours per day in urban area. The rate of increase of population is also different in rural and urban area for forecasting the population for the designed period.
The next criteria is the source. Generally when there is no water or the quality of water available at some place is not fit for drinking or its harnessing is not economical (very deep),water is pumped through pipe lines or conveyed through canals from distant places. For example water is carried through 204 km long Rajeev Gandhi Lift Canal originating from R.D 1109 of Indira Gandhi Main Canal in Rajasthan for Jodhpur city and many enroute villages. The Indira Gandhi Main Canal originates from Hari- Ke Barrage and flows by gravity for about 600 km.
The water in Rajeev Gandhi Lift canal is lifted at 8 places for about 200 meters for conveying it to Jodhpur. This involves a great expenditure on electricity, construction and maintenance of canal. Some portion of this canal is made up of mild steel pipes where the construction of canal was not economical. So all these aspects like surety of availability of water, quality of water, cost of treatment, cost of supply etc. are to be considered before making a final decision. Some of the water supply schemes are as follows:
Traditional Source scheme: In this scheme the traditional source of the water supply already existing in the village like an open well or the pond is electrified and pumping machinery is installed. The pumped water is distributed to the villagers by the existing small tanks near the wells. After commissioning the scheme it was handed over to the villagers to run at their own cost through the Panchayats (local bodies of the villages). But the schemes were not run by them successfully due to lack of interest and money. Government of Rajasthan has started a new project namely ‘Swajaldhara’ in which the villagers frame their own water supply schemes and pay 10% of the cost to the government. Government pay 90% and get the scheme executed and hand it over to the villagers to run it at their own cost under the guidance of the government. Many N.G.Os (Non-Governmental Organizations made voluntarily for the service of the society) help them for this purpose. At present this is running well in some districts of Rajasthan.
- Pump and Tank Schemes: In these schemes the government public health departments develop a source in the village itself. It may be an open well or a tube- well generally. One ground level reservoir (G.L.R.) is constructed and the pump installed on the source fills water in this tank. Public stand posts (P.S.Ps) are constructed by the sides of this GLR and public is allowed to fetch water from here free of cost but no hose connections are given.
- Regional Water Supply Schemes: When there is no feasible source of water in a village (water may be very deep or saline), then the water has to be carried from distant places like some other village well with enough potable water or some canal or river. So this is a combined scheme of many villages. Pipe lines have to be laid to carry water from the source to the benefited villages. So it is a costlier option. Water is generally supplied at one or two points in the villages free of cost. Some times connections to individual houses are also given depending upon the population and the paying capacity and willingness of the consumers.
- There are some regional water supply schemes which cater the needs of hundreds of villages alongwith the urban towns in Rajasthan like the Rajeev Gandhi lift canal water supply scheme, Ganddheli –Sahawa scheme, Bisalpur Ajmer, Jaipur scheme and many others. The Rajeev Gandhi Scheme originates from RD1109 of Indira Gandhi Main Canal, constructed and maintained by the Irrigation Department of Rajasthan. The Public Health Engineering Department of Rajasthan (PHED or more commonly known as Water Works) has constructed about 204 Km long Rajeev Gandhi lift canal. In this water is lifted at 8 places before it reaches to Jodhpur so it is known as a lift canal. The discharge in the first phase was about 200 cusecs which has been raised in the second phase for the increased population and addition of more and more villages.
- This is one example of a big Reg. Water Supply Scheme. Thousands of other Reg.W.S.S are running in Rajasthan because generally either there is no water or sline, brackish, fluoride water is there in most of the villages of Rajasthan. This option is very costly because of the capital cost of long lengths of conveying mains (canal or pipes), maintenance cost and the electricity cost of pumping in lifting of water. As a primary estimate the cost of raw water in Rajeev Gandhi lift canal comes as Rs. 40 per thousand litres and the government charges at the uniform rate of Rs. 4 per thousand litres from the average domestic consumer. One should realize it and conserve water.
- Piped Water Supply Schemes: These are generally for towns or big villages (urban areas). In these schemes house connections are given and the consumption is charged. The source may be in the locality or a distance source ( like Rajeev Gandhi lift canal for Jodhpur). R.C.C. Overhead tanks known as elevated service reservoirs (E.S.R) are constructed for the distribution of water through the distribution mains. First of all the raw water is treated by all means including disinfection (most important). Then pumped to ESRs and then distributed either for the whole day or at certain fixed time. The consumption is generally metered and charged on monthly basis. After some years the existing water supply schemes are reframed and executed. Such schemes are known as Reorganized Water Supply Schemes.
- Urban Water Supply Schemes: These are the schemes implemented for the urban areas. The main difference of urban and rural area is the population. Generally more than 10000 population is considered as urban area. The main difference in design of rural and urban water supply scheme is the rate of water supply. The design rate of water supply in rural areas as per the governments norms is 40 litres per capita per day except the 11 desert districts of Rajasthan for which it is 70 LPCD (including the cattle water demand). For urban area the rate is 135 litres minimum and it increases with the population. The other main difference is the house connections. In most of the rural water supply schemes water is supplied at a common point and people have to fetch it from this common place also known as public stand post. In urban water supply schemes every house is given a metered or flat rate service connection through which water is generally supplied intermittently (say twice in a day).
- The water obtained from a surface or ground source is treated and lifted in an elevated service reservoir. Then it is distributed through a properly designed and maintained distribution system. Though some of it is wasted in leakages but the loss should not be more than 10%. The water is also supplied for industrial and commercial purposes. Some of the water is always stored for fire fighting. As there is a depletion of ground water, and uncertainty of rainfall due to global warming and other reasons, it has become very difficult to maintain the urban water supply schemes these days.
Quality of Water
Quality of water is the most important aspect. There are international and national standards for the quality of water to be supplied for human consumption. The state governments may have a slight relaxation in the standards depending upon the local conditions but in general they are the same throughout the country. The main aim of the public health engineering departments or the environmental engineering departments as they are called these days is to supply safe and palatable (good in taste) water to the consumers. Water should also be free from any odour. The temperature of water should be reasonably good. It should neither be corrosive nor scale forming and should be free from minerals that can produce undesirable physiological effects. For achieving this ideal condition the minimum standards of quality are to be established.
The evolution of standards for the control of quality of public water supplies has to consider the limitations imposed by the local factors in the different regions of the country. As per the Manual on Water Supply and Treatment published by the Government of India, the main objective is to make water absolutely free from risks of transmitting disease, means safety is compulsory where as the other qualities are to be maintained within a specified range. For example water may have dissolved solids upto 500 mg per litre but cannot have any bacteria or other micro organism. Actually water is a very good carrier of many diseases producing organisms (pathogens) as there are all chances of its getting contaminated (infected by pathogens).
If a small drop of urine or fecal matter (excreta, nightoil) is mixed in a body of water (canal, pond etc.) and the person contributing it has some disease like cholera, gastroentitis, infectious hepatitis jaundice, typhoid, etc., it will infect the stream. Anybody using that water without treatment (disinfection) is liable to catch the same disease. Sometimes the foul waste water (from latrines, toilets etc.) goes down the earth and gets mixed (at a shallow depth) with the ground water it pollutes it. If this ground water lifted by a hand pump or a tube-well is used again without disinfect ion it shall cause disease in the person using it. Sometimes the dissolved salts may produce some other diseases like fluorosis (due to excessive fluoride) mathemaglobinemia (blue baby disease) due to excessive nitrates in, infants) etc. So water must not have the physical, chemical and bacteriological parameters beyond limits.
Characteristics of Water
To ensure the quality of safe drinking water (potable water) the water is to be tested for its physical, chemical and bacteriological characteristics.
- Physical Characteristics:
- Temperature: It can be measured by a thermometer. The temperature should be suitable to the human beings depending upon the climatic and weather conditions. An average temperature of 15°C is generally suitable.
- Turbidity: The muddy or cloudy appearance of clay or such other particles that presents hindrance to the path of light is known as turbidity. It may not be harmful but even then from aesthetical point of view it should not exceed the allowable value. The turbidity is measured by a turbidity rod or a turbidity meter with physical observations and is expressed as the suspended matter in mg/l or ppm (part per million). The standard unit of turbidity is that which is produced by 1 mg of finely divided silica in one litre of distilled water. The turbidity in excess of 5 mg/l is detectable by the consumer and is hence objectionable. It is measured in the laboratory by Jackson ,Baylis or such other turbiditymeters.
- Colour: The colour is imparted by dissolved organic matters from decaying vegetation or some inorganic materials such as coloured soils (red soil) etc. The algae or other aquatic plants may also impart colour. Again it is more objectionable from aesthetics point of view than the health. The standard unit of colour is that which is produced by one milligram of platinum cobalt dissolved in one liter of distilled water. Colour is measured in the labs by Nessler’s tubes by comparing the sample with the known colour intensities. More precisely tintometer measures it.
- Taste and odour: The dissolved inorganic salts or organic matter or the dissolved gases may impart taste and odour to the water. The water must not contain any undesirable or objectionable taste or odour. The extent of taste or odour is measured by a term called odour intensity which is related with threshold odour, which represents the dilution ratio at which the odour is hardly detectible. The water to be tested is gradually diluted with odour free water and the mixture at which the detection of taste and odour is just lost is determined. The number of times the sample is diluted is known as the threshold number. Thus if 20 ml of water is made 100 ml (until it just looses its taste or odour) then the threshold number is 5. For domestic water supplies the water should be free from any taste and odour so the threshold number should be 1 and should not exceed 3.
- Specific conductivity of water: The specific conductivity of water is deter- mined by means of a portable dionic water tester and is expressed as micro- mhos per cm at 25°C. Mho is the unit of conductivity and is equal to 1 amper/ 1 volt). The specific conductivity is multiplied by a co-efficient (generally 0.65) so as to directly obtain the dissolved salt content in ppm..
Chemical analysis of water is done to determine the chemical characteristics of water. This involves the determination of total solids, suspended solids, pH value, hardness, chlorides, nitrogen content, iron, manganese and other contents, dissolved gases etc.
- Total solids and suspended solids: The total amount of solids can be deter- mined by evaporating a measured sample of water and weighing the dry residue left. The suspended solids can be determined by filtering the water sample and weighing the residue left on the filter paper. The difference between the total solids and the suspended solids will be the dissolved solids.
- pH of water: pH is the negative logarithm of hydrogen ion concentration present in water. The higher values of pH mean lower hydrogen ion concen- trations and thus represent alkaline water and vice versa. The neutral water has same number of H+ and OH– ions. The concentration of both ions in neutral water is 10–7 moles per liter. The neutral water will therefore possess a pH equal to + –7 7 log10 (1/H ) = log10 (1/10 ) = log10 10 = 7 If an acid is added to neutral water the number of hydrogen ion increases and thus the pH reduces. Similarly, if an alkali is added the number of hydroxyl ion increases thus reducing the hydrogen ion (as their product is constant, = 10–14 mole/liter) and the pH increases. Hence, if the pH of water is more than 7 it is alkaline and if it is less than 7 it is acidic. Generally, the alkalinity in water is caused by the presence of bicarbonates of calcium and magnesium, or by the carbonates or hydroxides of sodium potassium calcium and magnesium. Some of the compounds which cause alkalinity also cause hardness. Acidity is caused by the presence of mineral acids, free carbon dioxide, sulphates of iron and aluminium etc.
- Hardness of water: Hardness in water prevents the formation of sufficient foam when used with soap. It is caused by certain dissolved salts of calcium and magnesium which form scum with soap and reduce the formation of foam which helps in removing the dirt from clothes. These salts keep on depositing on the surface of boilers and thus form a layer known as scale which reduces the efficiency of the boilers. The hardness is known as tem- porary hardness if it is due to the bicarbonates of calcium and magnesium as this can be easily removed by boiling water or adding lime to it. By boiling the carbon dioxide gas escapes and the insoluble carbonates are deposited (which cause scaling). If sulphates, chlorides and nitrates are present they cannot be easily removed by boiling and so such water requires water soft- ening methods and this type of hardness is known as permanent hardness.
- Chlorides: Chlorides are generally present in water in the form of sodium chloride and their concentration above 250 mg/l produces a salty taste in drinking water. The chlorides can be measured in water by titrating the water with standard silver nitrate solution using potassium chromate as indicator.
- Nitrogen content: The nitrogen in water may occur in one or more forms of the following:
- Free ammonia
- Albuminoid nitrogen
The free ammonia indicates very fast stage of decomposition of organic matter (thus indicating fresh pollution); albuminoid nitrogen represents the quantity of nitrogen present in water before the decomposition of organic matter has started, the nitrites indicate the partly decomposed organic matter (the con- tinuation of decomposition) and the nitrates indicate the presence of fully oxidized organic matter (means the prior pollution condition). In potable water the free ammonia (undecomposed organic matter should not be more than 0.15 ppm, and the albuminoidal nitrogen should not be more than 0.3 ppm. The nitrogen may remain in the form of nitrates but that too should not be more than 45 ppm as a higher concentration causes blue baby disease in the infants. Actually the nitrates act with the haemoglobin in the blood (which imparts red colour) and reduce it thus converting the colour of skin to blue (impure blood) and thus making them ill and in extreme cases they can die. Nitrate is measured either by reduction to ammonia or by matching the colours produced with phenoldisulphonic acid.
- Metals and other chemical substances: Various metals and minerals may be present in water like iron, manganese, copper, lead, cadmium, arsenic, barium, selenium, etc. The allowable limits for them are as shown in the above tables. If the concentration of these metals and minerals exceeds the permissible limits they have certain harmful effects on the human health. Higher concentrations of iron and manganese may cause discoloration of clothes washed in such waters. They may cause incrustation in water supply pipe lines due to deposition of ferric hydroxide and manganese oxide. Lead and barium salts are toxic and thus very low concentration of these salts is permissible. Arsenic is a well known poison and as such extremely low concentration (0.05 ppm) is permitted. Most of the ground water in Punjab is having arsenic more than the permissible limits because of the industrial waste water pollution. High quantities of copper may badly affect human lungs and other respiratory organs.
- Dissolved gases: Various gases like CO2, O2, N2, H2S and CH4 etc. may be present in dissolved form in water. H2S even in small concentration gives bad taste and odour. CO2 indicates biological activity. Oxygen is generally ab- sorbed by water from the atmosphere. Its saturation concentration depends upon temperature. The organic matter may be present in water due to the disposal of waste water in it. Organic matter is instable and has a tendency to become stable i.e. to be inorganic matter. This conversion is known as decomposition of organic matter and the process is bio-chemical. As it takes place by bacteria (bio means living) and the conversion is extra cellular enzymatic reaction so it is known as a bio-chemical reaction. The demand of oxygen imposed by the aerobic (working in presence of oxygen) bacteria is known as the Bio Chemical Oxygen Demand (BOD). This BOD reduces the dissolved oxygen content of the water. So if the DO of water is found to be less than the concentration DO it indicates the water pollution. The BOD of treated water should be nil.
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