While estimating the water demand, the above factors should be considered e.g. the size of the city; its population does matter when estimating the water demand. The more the size of population, more will be the demand. Estimation of water demand is necessary to:

1.     Calculate design flow

2.     Determine the pumping power of machines to be used

3.     Reservoir capacity

4.     Pipe capacity

To estimate water demand, following parameters must be determined or calculated.

1. Average daily water consumption: It is based on complete one year supply of water. It is the total consumption during one year, divided by the population. q = (Q / P x 365) lpcd (liters per capita per day)

2. Maximum daily consumption: It is the maximum amount of water used during one day in the year. This amount is 180% of the average daily consumption MDC = 1.8 x Avg. daily consumption. It is usually a working day (Monday) of summer season.

3. Maximum weekly demand: The amount of water used by a population during a whole single week in a study span of 1 year.

Maximum   Weekly       demand       =       1.48   x        Avg.            D.      C

Maximum   Monthly      demand       =       1.28   x        Avg.            D.      C

Maximum   Hourly        demand       =       1.5     x        Avg.            D.      C

 Maximum daily demand = 1.8 x Avg. D. C

4. Fire water demand | Fire Demand: Theamount of water usedfor fire fighting is termed as fire demand. Although, the amount of water used in fire fighting is a negligible part of the combine uses of water but the rate of flow and the volume required  may  be  so  high  during  fire  that  it  is  a  deciding  factor  for  pumps, reservoirs And distribution mains.

Minimum    fire    flow   should         be      500    gpm   (1890 L/m)

Minimum    fire    flow   should         be      8000  gpm(32,      400    L/m)

Additional flow may be required to protect adjacent buildings.

SOURCES OF FRESH WATER

The quantity of water required for a community depends upon:

1.     Forecasted population

2.     Types and variation in demand (e.g. seasonal variation)

3.     Maximum demand (Per day/Per month)

4.     Fire demand

5.     Rural demand and supplies

6.     Appropriate / Available technology

Main sources of water are

 1.     Surface water sources: Lakes impounding reservoirs, streams, seas, irrigation canals

2.     Ground water sources: Springs, wells, infiltration wells

Factors affecting the use of water

 Size of the city

Industry and commerce

Climate

Time of the day

Day of the week or month