The water should reach each consumer and therefore it should reach on
the uppermost storey. The pressure which is required to be maintained in
the distribution system depends upon the following factors (Garg,
1994).
1. The height of highest building up to which water should reach without boosting.
2. The distance of the locality from the distribution reservoir.
3. The supply is to be metered or not. Higher pressure will be required to compensate for the high loss of head in meters.
4. How much pressure will be required for fire-hydrants?
Sometimes
the design pressure is determined from the firefighting requirements
(Jan, 2002.). In some cities and towns the firefighting squads are
equipped with pumping sets fitted on their vehicles for lifting the
water at the site itself. At such places the design pressure may be
determined by the minimum required by the consumers. But in most of
towns in India the people living at 2nd, 3rd or 4th storey face lots of
difficulties due to non-supply of water in their storey’s. At such
places small lifting pumps may be individually used which directly pump
the water in their water lines. In multistoried structures the following
pressures are considered satisfactory according to Water Aid (2002)
Guidebook to Global water issues, (Retrieved July 19, 2010.).
1. Up to 3 storey - 2.1 kg/ cm2
2. From 3 to 6 storey - 2.1 to 4.2 kg/ cm2
3. From 6 to 10 storey - 4.2 to 5.27 kg/ cm2
4. Above 10 storey - 5.27 to 7 kg/ cm2
While designing pipes of distribution systems the following points should be kept in mind, Water Aid (2002):
1) The main line should be designed to carry 3 times the average demand of the city.
2) The service pipes should be able to carry twice the average demand.
3) The water demand at various points in the city should be noted.
4) The lengths and sizes of each pipe should be clearly marked on the site plan along with hydrants, valves, meters, etc.
The minimum velocity in pipe lines should not be less than 0.6 m/sec and maximum velocity should not be more than 3 m/ sec.
For
best results the velocities in different pipes should be as follows
Water Aid (2002) Guidebook to Global water issues. (Retrieved July
2010):
Diameter of pipes Velocity
1. 10 cm 0.9 m/sec
2. 15 cm 1.21 m/sec
3. 25 cm 1.52 m/sec
4. 40 cm 1.82 m/sec
