Water demand is the measure of total amount of water used by the consumers within the enitre system. Several factors influence the amount of water used daily, monthly, annually and yearly. A water system is developed to meet this water demand without interruption and rain.
Daily demand = V/365
Average daily demand by a person = V/ (365 X P) lpcd
lpcd –> litre per capita per day (or) litre per person per day
Types of Water Demand In A City
1. Domestic Demand
As per GOI domestic demand is 135 lpcd (average per capita water demand per day) and the 80% of total consumption is converted into sewage.
The domestic need of water also varies as per the income group. In low income group (LIG) there is 135 lpcd of water consumption whereas in high income group (HIG) there is 200-225 lpcd of water consumption.
As per IS: 1172-1993 average Indian town water demand –
- Without flushing system (LIG)
Domestic – 135 lpcd (50-60%)
Industrial and commercial – 70 lpcd (20-25%)
Public use – 10 lpcd (5-10%)
Loses and theft – 55 lpcd (15-20%)
- With flushing system (HIG)
Domestic – 200 lpcd (50-60%)
Industrial and commercial – 70 lpcd (20-25%)
Public use – 10 lpcd (5-10%)
Loses and theft -55 lpcd (15-20%)
2. Industrial Demand
Average industrial area demand is 50 lpcd. Whereas in high industrial area is increases nine folds summing upto 450 lpcd.
3. Commercial Demand
Average commercial demand is 20 lpcd while in highly commercialised areas and zones it is 50 lpcd.
- Industrial and commercial demand
Offices – 40-45 lpcd
Day schools – 45-90 lpcd
Hostels – 180 lpcd
Restaurants – 70 litre/ seat
Hospitals – (<100 beds) 340 litre/ bed
(>100 beds) 450 litre/ bed
Bus-stand, railways, airports – 70 lpcd
4. Fire Demand
For,
P (population) = 50 lakh
Q (discharge) = 1100 litre/ min (for 5-6 hrs.)
Fire demand = 1 lpcd
As per the population the fire demand varies.
If population exceed 2 lakhs then a provision for 54600 litre/ min maybe made with an extra provision of 9100 to 36400 litre/ min for second fire.
Some empirical formula to calculate fire demand
1. National Board Formula (Writer’s Formula)
P ≤ 2 lakh
Q = 4637 √P (1 – .01√P)
where, Q (litre/min)
P (in thousands)
2. Kuichling’s Formula
Q = 3182 √P
where, Q (litre/min)
P (in thousands)
3. Freeman’s Formula
Q = 1136 (P/10 + 10)
5. Theft and Loses
15% of total demand of water of a city is wasted or lost in the form of theft or leakage.
6. Public Use
5% of total demand of a city is used in public places like sulabh kendra etc.
Factors Affecting Water Demand
- Increase in industrial activity results in increase in the demand of water.
- Climatic condition like summer demands an increase in demand of water due to requirement for cooling. During winters in freezing and sub-freezing zone there is an increase in demand due to requirement of continuous flow of water to avoid freezing.
- On the basis of method of charging / costing demand varies. If it is fixed then water use increases as there is unmeasured use of water. Whereas in case of water metre demand of water decreases due to pay and measure.
- If the type of supply is continuous (24 hr supply) then the demand increases. On the other-hand if the supply is intermittent then also it increases as there is wastage of stored water.
- As the pressure in supply system increases demand also increases.
- With increase in population and size of city demand also increases.
- If sewage system is present then demand of water is increased and if sewage system is absent then demand is also low.
- The quality of water plays an important role because as the quality increases so does its demand.
