BASICS, SOURCES OF WATER, WATER DEMAND

Raw Water Source

The various sources of water can be classified into two categories:

1. Surface sources, such as

a. Ponds and lakes;
b. Streams and rivers;
c. Storage reservoirs; and
d. Oceans, generally not used for water supplies, at present.

2. Sub-surface sources or underground sources, such as

a. Springs;
b. Infiltration wells ; and
c. Wells and Tube-wells.

Water Quantity Estimation

The quantity of water required for municipal uses for which the water supply scheme has to be
designed requires following data:

1. Water consumption rate (Per Capita Demand in litres per day per head)

2. Population to be served.

Quantity= Per capita demand x Population


Water Consumption Rate

Domestic Consumption  : 135 lpcd ( 200 if full flush system )

industrial demand : 70 lpcd

public demand : 10 lpcd

losses & thefts : 55 lpcd

Offices , Schools : 45 - 90 lpcd

Residential, Hospital : 180 lpcd

Restorants, Railways : 70 lpcd

Fire Fighting Demand:

The per capita fire demand is very less on an average basis but the rate at which the water is

required is very large. The rate of fire demand is sometimes traeted as a function of population

and is worked out from following empirical formulae:

Factors affecting per capita demand:

a. Size of the city: Per capita demand for big cities is generally large as compared to that

for smaller towns as big cities have sewered houses.

b. Presence of industries.

c. Climatic conditions.

d. Habits of people and their economic status.

e. Quality of water: If water is aesthetically & medically safe, the consumption will increase

as people will not resort to private wells, etc.

f. Pressure in the distribution system.

g. Efficiency of water works administration: Leaks in water mains and services; and

unauthorized use of water can be kept to a minimum by surveys.

h. Cost of water.

i. Policy of metering and charging method: Water tax is charged in two different ways: on

the basis of meter reading and on the basis of certain fixed monthly rate.

Maximum daily demand = 1.8 x average daily demand

Maximum hourly demand of maximum day i.e. Peak demand

= 1.5 x average hourly demand

= 1.5 x Maximum daily demand

= 1.5 x (1.8 x average daily demand)

= 2.7 x average daily demand

= 2.7 x annual average hourly demand

Population Forecasting Methods

1. Arithmetic Increase Method : used for cities attained saturation 
2. Geometric Increase Method : young and rapidly growing cities
3. Incremental Increase Method
4. Decreasing Rate of Growth Method
5. Simple Graphical Method
6. Comparative Graphical Method
7. Ratio Method
4. Logistic Curve Method