• APSEd

Water Demand and its Types | Fire Demand Formulas |Design Capacities of Water Supply Systems

Water demand is the amount of water required to satisfy the needs of a population present or to be present (forecasted) in an area. Before planning any water supply projects for an area it becomes absolutely necessary to calculate the total demand for water in that area so as to design the water supply systems with such capacity. Unit for water demand measurement and types of demand are discussed further.


What is lpcd


lpcd stands for litre/per capita/per day, which is the amount of water required in litres per person per day.


Types of Water Demand


Types of water demand
Types of water demand

1. Domestic water Demand


According to IS1172: 1993, the water demand for Indian towns/cities shall be based on two categories, namely,

  1. Full flushing system / High-income group

  2. Low-income group

Water required by both these groups for different purposes is shown below.

Purpose

High-Income Group (lpcd)

Low-Income Group (lpcd)

Drinking

5

5

Cooking

5

5

Bathing

75

55

Washing cloth

25

20

Washing utensils

15

10

Washing house

15

10

Garden

15

-

Flush

45

30

Water Demand for High-Income group and Low-Income group


Totalling the above values, we get water demand for each group as,

High Income group = 200 lpcd

Low Income group = 135 lpcd


2. Industrial Demand


It depends on the type of industries present in an area/town and usually varies from 50 to 450 lpcd.


3. Institutional and Commercial Water Demand


It is the water required for institutional and commercial establishments like schools, colleges, malls, etc. and it usually varies from 10 to 20 lpcd.


4. Water for Public Uses


It is the water required for public usage such as gardening, fountains, etc. and it completely depends on the area where the water supply system is being developed.


5. Fire Demand


It is the amount of water required for fire fighting purposes if in case a fire breaks out in an area. This water is required to be available at a pressure of about 100 to 150 kN/m^2 or 10 to 15m head of water. Fire demand is not calculated for smaller towns where the population is less than 50,000. For larger cities, fire demand is calculated using various formulas which are discussed further.


Fire Demand Formulas


1. Kuichling's Formula


Q = 3182 * √P,

where,

Q - water required in litres/minute

P - population in 1000s (i.e., if population is 1,00,000 then P = 100)


2. Freeman's Formula

Q = 1136 * [(P/10)+10],

where,

Q - water required in litres/minute

P - population in 1000s