Water Demand-Fire Demand-Water Supply System

Water demand or demand for water or draft is the amount of water required for consumption. Here, the measurement of water demand is necessary in order to design a water supply system for a particular area or community.
The article explains, water demand, its measurement, types of water demand and its standard values.

Water Demand-Water Supply System-Environmental Engineering
Water Demand-Water Supply System-Environmental Engineering



Measurement of Water Demand or Draft

The water demand is measured in lpcd i.e. liters per capita per day. Per capita here represents per person. Hence, lpcd is the amount of water required per person per day in liters. Lpcd is calculated by the formula below:

        1lpcd = [Total Yearly Consumption or Population ]/ [ 360 x Design Population]


Types of  Water Demand

Different types of water demand based on the Indian Standard code IS-1192:1993 are:
  1. Domestic Demand
  2. Industrial /Commercial Demand
  3. Public Utilities
  4. Thefts or Leakages
The consumption rate of each demand mentioned above varies with whether the family is a LIG family or a HIG family [ Low Income and High Income Group]. The values and percentage consumption are explained in the table below.

                      Table.1. Water Demands for Different Use in lpcd; As per IS:1192-1993
SL.No
Type of Demand
Percentage Consumption
Low Income Group (lpcd)
High Income Group(lpcd)
1
Domestic Purpose
50-60%
135
200
2
Industrial or Commercial
20-25%
70
70
3
Public Utilities
5-10%
10
10
4
Thefts & Wastage
15-20%
55
55

Note: There is an exceptional case where, the water demand for Hotels, schools and small organizations, the water demand is 135lpcd.

Fire Demand

The water required for unexpected fire accidents and undesirable situation with fire is already designed during the water demand planning system. The demand is calculated based on empirical formulas. For all the formulas given below, Q is the discharge calculated in liters per minute and P is the population measured in thousands.

1. Kuichling's Formula

Q = 3182P1/2

2. Buston's Formula

Q = 5663P1/2

3. Freeman's Formula

Q = 1136[0.2P + 10]

4. National Board of Underwater Formula

Q = 4637P1/2[1 - 0.01P1/2]

Maximum Daily Demand (MDD) and Maximum Hourly Demand (MHD)

Before determining MDD and MHD, we need to understand, what is average daily demand (q).

q = Px;
Where, P= Population, x = water in lpcd

1. Maximum Daily Demand (MDD) = Q = 1.8q
2. Maximum Hourly Demand ( MHD) = Q = 1.5MDD = 2.7q





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