POINTS TO BE CONSIDERED FOR A PROTECTED WATER SUPPLY SCHEME (WSS)
The following factors should be kept in view in water supply for particular place.
i) THE SOURCE: Source should be selected which may sufficiently provide the water in all the seasons. The sources may be wells steams, natural lakes, deep ponds in rivers, reservoirs, perennial rivers etc…
ii) QUANTITY OF WATER: It can be estimated by considering need for present population and future population growth during the design period also some quantity of water will be required for fire fighting, public conveniences street washings and horticultural purposes. In addition to these some water is usually wasted by the consumers. Thus the total quantity way of water may be estimated for a particular locality considering all the above factors.
iii) CHECK CALCULATION: After the above calculations are completed, designer should again confirm whether the source of water will provide the required amount of water especially in summer season of the driest year.
iv) DISTANCE AND DIFFERENCE IN ELEVATION: The designer should see distance and difference in elevation in a town with respect to source of water. As far as possible the water should be under enough pressure in service pipes so that it may reach upto 10-15m.
v) IMPOUNDING RESERVOIR: May only be provided if its provision at higher elevation is not economical.
vi) QUALITY OF WATER: After this the quality of water should be tested the treatment units should be installed according to degree of pollution in the source.
vii) METHODS OF PURIFICATION: The methods of purification of water for drinking purposes may be divided into 5 parts viz.
a) SCREENING: in which the fine and coarse particles, rags, papers, etc… are separated through fine and coarse screens.
b) PLAIN SEDIMENTATION: in which the sedimentation of set liable solids in large tanks is affected.
c) COAGULATION OR CHEMICAL PRECIPITATION: This is adopted when there is much turbidity. The alum solution is generally mixed in water and the precipitation is formed which is later separated.
d) FILTRATION: in which water is passed through layers of stones and sand.
e) DISINFEC TION: in which the pathogenic bacteria are destroyed.
NOTE: In addition to these some special methods like softening, aeration, iron removal etc….. are also resorted to remove colour, bad taste smell etc….
viii) SERVICE RESERVOIR: Pure water may be stored at a higher elevation in the town which is called a service reservoir. From these reservoir the water may be supplied in the hours of peak demand
ix) DISTRIBUTION SYSTEM: the water from the service reservoir is served to consumers through a network of mains, sub mains, laterals called as distribution network system.