January 4, 2019

Water is a basic need of all human beings. Inadequate & contaminated water can create social problems.

The cleanliness and hygiene of people, depends on the adequate and timely supply of good quality water.

The local municipalities arrange and maintain the water supply of a city. These municipalities lay their rules and regulation for ensuring the adequacy and the quality of waters in all the localities.

A construction project needs large quantity of water. Initially water is required for the construction work and the workers. After completion of the project, water is required for the residents, occupants of the project. Therefore a systematic water supply arrangement shall be designed to avoid wastage and to ensure the continuity of supply.

The water supply system is designed on the following lines.

  1. Estimating exact demand of water.
  2. Designing the underground & overhead water tanks for their capacity, size and locations.
  3. Designing the pumping arrangements with pump capacities.
  4. Designing the locations for various valves such as air release valves, non- return valves etc.
  5. Designing all the measures required to avoid leakage, bursting of lines, contamination of water etc. A simple example will help to understand the method of design.

Consider a residential project having 3 buildings with 28 flats each. Assuming 5 occupants in each flat;

The total water demand per day is

=3no.(buildings)x28 no.(flats) x 5no.(occupants/flat)x135 lit./day/capita

= 56700 liter /day

+5670 liter / day (Added 10 % for common uses like firefighting reserves, evaporation & handling losses)

= 62370 liter / Day

= Say 62000 liters / Day

A suitable water connection is taken from the common water supply of the municipal Authority. Water supply is taken into an underground water storage tank located suitably.

The underground water tank (U.G.tank) is designed for a minimum capacity of 1.5 days demand. Therefore the capacity of U.G. tank = 1.5 x 62000 liter

= 93000 liters

= 93 cubic meter

A tank of size 8 m x 5 m x 2.4 m (clear height) posses the capacity of 96 cubic meters. Therefore provide a water tank of size 8m long x 5m wide x 2.4 m height (including freeboard )will serve the purpose.

Actual capacity = 96000 liter (96cu. Meter).

The required size can be changed as per the site conditions without changing the capacity. The U.G.

Tank is built as per suitability of design, either in B.B.M. or in R.C.C. work. The tank is covered by R.C.C. slab. Manhole chambers with covers, ladder for entering inside for cleaning, air vent at suitable place and a sump at bottom corner for foot valve of pump etc. are the basic requirements of a U.G.W.T.

The water collected & stored in the U.G.W.T. is then lifted by pumps and rising main line to the O.H.W.T. The selection of pumps is based on, suction & discharge head as required. The O.H.W.T.’s are designed for a capacity of 1 day’s domestic demand plus the minimum firefighting reserve stock as per the rules.

In the example discussed above for one building having 28 flats, the water demand & hence the capacity of the O.H.W.T. is worked out as follows.

Domestic Demand for one day = 28 No. X 5 No. x 135 liter / day

= 18900 liters

+10000 (for firefighting purpose)

= 28900 liters

Say 29000 liters

= 29 cu.m

Usually the O.H.W.T. constructed in R.C.C. work, is provided on the top of the staircase block so as also to work as a roof slab of staircase. The staircase block is usually of the size 5 m x 2.5 m. Therefore a

O.H.W.T. of size 5 m x 2.5 m x 2.5 m having a capacity of 31.25 cu.m (Including freeboard) will suffice the purpose.

The water supply lines from the O.H.W.T. are provided, as per the designed pressure and diameter, to individual unit (flat, shop etc)


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