Water Distribution

Method of Water Distribution

Water is forced in the distribution system in the following ways

(i) Gravitational system
(ii) Direct pumping
(iii) Combined system

Gravitational System

• This method of water distribution is cheapest among other systems of water distribution.
• In this method, water from high level source is distributed at lower levels by simple action of gravity without pumping.
• This system works well where lakes are available at top of a hill.

Direct Pumping

• In this, the treated water instead of pumping to the service or distribution reservoir, is directly pumped to the distribution mains.
• Since, supply is done directly to the distribution mains and services, high lift pumps are required to overcome the friction losses at different stages and to have some residual head at distribution points so that water may rise at higher storey of building.
• Since, water demand varies with time, pumps are required to be run at variable speed to meet water requirement at different time periods
• Due to variable speed, the pumps do not work at their maximum efficiency; hence, the system is not so economical.

Combined System

• In this system of water supply, there is combined actions of gravity and pumps.
• In this system, the treated water is pumped and stored in an elevated distribution reservoir or tank and from the distribution tank, it is fed to the distribution system by the action of gravity.
• Pump works at constant and convenient schedule and the pressure can be maintained uniformly during the supply.

PRESSURE IN THE DISTRIBUTION SYSTEM

Pressure in the distribution system depends on the following factors:

(i) Domestic use
(ii) Fire demand
(iii) Economic considerations
(iv) Topography
(v) Future demand

For domestic services, the supply pressure depends upon number of storeys upto which water is to be lifted without additional use of booster pumps. For residential area, a pressure of 0.6 to 15 kg/cm2 is considered to be sufficient. Providing greater pressure in pipe than the required value makes the system costly. Following minimum residual pressure should be provided at the ferrule points.

Single storey buildings : 7 m above ground level
Two storey buildings : 12 m above ground level
Three storey buildings : 17 m above ground level

The distribution system is not designed for residual pressure more than 22 m. Hence, for high rise buildings booster pumps should be provided.