ESTIMATION OF WATER DEMAND
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
Time of the day
Day of the week or month