For average Indian towns or cities the rate of demand of water varies from 100 to 300 litres per head per day. The variation in the rate of demand of water is due to several factors which must be carefully studied and analysed before fixing the rate of demand of water for a particular town or city.
The various factors affecting the rate of demand of water are as listed below:
Factor # 1. Climatic Conditions:
The requirement of water is more at places having hot and dry climate than at places having cold and humid climate. This is so because at places having hot and dry climate more water is required for bathing, washing of clothes, air coolers, air conditioning, lawn watering, gardening, etc.
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Similarly the requirement of water is more in summer than in winter. Further in extremely cold climates water may be wasted due to taps being always kept open to avoid freezing of pipes, which may result in increased rate of consumption.
The rate at which water is supplied to the consumers may also affect the rate of demand of water. If the rates at which water is supplied are high, lesser quantity of water may be consumed by the people, and vice versa. However, the general observation is that the consumption of water reduces only slightly as the cost is increased.
Factor # 3. Pressure in the Distribution System:
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The consumption of water increases with the increase in the distribution pressure. This is due to increase in loss and waste of water at high pressure. For example, an increase of pressure from 196 kN/m2 (2 kg/cm2) to 294 kN/m2 (3 kg/cm2) may lead to an increase in consumption of water by about 25 to 30 per cent.
Factor # 4. Economic Status of Consumers:
The consumption rate of water is directly dependent upon the economic status of the consumers. Rich and upper class people generally consume more water due to their better standard of living. On the other hand middle class people have average rate of consumption of water while the poor slum dwellers have a much lower rate of water consumption.
Factor # 5. Number of Commercial Establishments and Industries:
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In general the presence of commercial and other establishments and industries in a town or city would increase the rate of demand of water. The rate of demand of water would further increase with the increase in the number of such establishments and industries. However, if the industries develop their own water supply system, then there may not be much increase in the rate of demand of water for the public water supply system.
Factor # 6. Method of Charging—Metered or Unmetered Water Supply System (or Policy of Metering):
The public water supply system may be either metered or unmetered. In the case of metered water supply, meters are fitted at the head of the individual house connections, which record the quantity of water actually consumed by the consumers. The consumers are charged for the actual quantity of water consumed by them as recorded by the meters.
As such with metered water supply the consumers use water carefully with minimum wastage, resulting in a reduced water use. On the other hand in the case of unmetered water supply the consumers are charged at a fixed monthly flat rate irrespective of the quantity of water consumed by them.
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Thus with unmetered water supply the consumers are tempted to use water more liberally resulting in a lot of wastage of water. The installation of meters therefore generally reduces the rate of demand of water.
However, there are several points for and against the installation of meters in a water supply system which are given below:
Points for the Installation of Meters:
(i) The consumer is required to pay only for the quantity of water he actually uses.
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(ii) Wastage of water is reduced.
(iii) The reduction in consumption of water results in reducing loads on water purification plants, pumps, sewers, etc.
(iv) The points of leakage may be more easily located.
(v) The careful consumer pays less and the careless consumer pays more.
(vi) When the quantity of water available is limited and the cost of operation is high, metering of water supplies provides the optimum utilisation of water.
Points against the Installation of Meters:
(i) There is appreciable loss of pressure through meters which adds to the cost of pumping.
(ii) Metering is quite expensive because a lot of money is to be spent to buy, to install, to read and to maintain the meters.
(iii) The limited use of water may result in unhygienic conditions and diseases.
(iv) Gardening is diminished which affects the economy and the general appearance of the town or city.
(v) The money required to be spent on meters might better be spent on improvement of water supply scheme.
(vi) Wastage of water can be more economically checked by inspection than by meters.
(vii) Cost and space required for setting up of meters may be prohibitive and are certainly restrictive.
If the quality of the supplied water is good, it will be consumed more, because the consumers will consider it safe for use and they will use it liberally for various purposes. Moreover, when good quality water will be supplied, the consumers will not use water from other sources such as private wells, hand pumps, etc. Thus in general the rate of demand of water increases with the improvement in the quality of the supplied water.
If a town or city is provided with a sewerage system, more water will be required for civic or public purposes. The residents of this town or city will also require more water for flushing sanitary units such as urinals, water closets, etc. Thus provision of sewerage system for a town or city increases the rate of demand of water.
Factor # 9. Size of Town or City:
In general bigger is the town or city, higher is the rate of demand of water, and vice versa. This is so because big towns or cities are invariably provided with sewerage system for which large quantity of water is required. The large quantity of water is also required for various other civic or public purposes for maintaining clean and healthy environment in big towns or cities.
Further the high standard of living for the residents of a big town or city also leads to a higher rate of demand of water due to large quantity of water being required for domestic use. Table 2.9 gives the average rates of demand of water for the Indian towns or cities of various populations. However, the presence of a water-consuming industry in a town or city may result in a higher rate of demand of water, even if the town or city is small.
Factor # 10. System of Supply of Water:
The water may be supplied either intermittently, i.e., for limited periods during certain fixed hours of the day, or continuously for all the 24 hours of the day. It is claimed that with intermittent supply of water the rate of demand of water is less, because the water being available for a shorter duration the leakage losses and the wastage of water by various reasons are considerably reduced.
However, in several cases with intermittent supply of water there is no much reduction in the rate of demand of water because of the following two reasons:
(i) With intermittent supply of water there is a tendency of many consumers to store water for use during non-supply period. However, this previously stored water is thrown away in order to collect fresh water when the supply is resumed. This results in waste of water.
(ii) During non-supply period the water taps are kept open and when the supply starts the water flowing through the open taps remains unattended, which results in waste of water.