Demand and Treatment of Water

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  • Topic: Chlorine, Water purification, Water
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  • Published : March 14, 2013
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Water Treatment

Water Demand
• Various types of water demands for a city
– Domestic water demands
– Commercial & industrial demand
– Fire demand
– Demand for public uses
– Compensate losses demand

Water Demand
• Domestic water demand
– It depends on the habits, social status, climatic conditions and customs of the people.
– The domestic consumption of water under normal conditions is considered to be about 135 LPCD (IS 1172-1971)
– The details of domestic consumption per person are as below: •

Cloth washing
Utensils washing
House washing
Flushing of latrines
» Total

55 L
20 L
10 L
10 L
30 L
135 L/

For rural water supply with stand post – 40 LPCD
For rural water supply with house connection 70 – 100 LPCD

Water Demand

Commercial and Industrial Demand
– The water demand for commercial and public places may be up to 45 LPCD
– Water supply requriements for few public buildings (IS 1172-1963) •

Factories with bathrooms
Factories without bathrooms
Hospitals, no of beds < 100
Hospitals, no. of beds > 100
Restaurants (per seat)
Hotels (per bed)
Cinema Hall (per seat)
Schools (day schools)
Boarding schools

340 LPCD
450 LPCD
135 LPCD
135 LPCD

– The water requirement for the industries differs from industry to industry and generally considered as 20 to 25% of the total demand of the city.

Water Demand

Fire demand
– During fire breakdowns large quantity of the water is required for throwing it over the fire to extinguish it.
– Hence, provision is made in the water works to supply sufficient quantity of water or keep as reserve in the mains for this purpose.
– Fire hydrants are provided on the mains at 100 to 150 m apart for this purpose.
– The quantity of water required for fire fighting is calculated using following empirical formulae:
• Kuichling’s formula :
• Buston’s formula :
• CPHEEO formula:

Q = 3182 (P)1/2
Q = 5663 (P)1/2
Q = 100 (P)1/2 (for P > 50000)

– Where, Q – quantity of water, L/min; P – Population in thousands

Water Demand
• Demand for public use
– Water is required for public utility purposes such as washing and sprinkling on roads, lawns, cleaning sewers, beautification
purposes, such as, fountains and impoundments, etc.
– The provision of about 5% of the total consumption is made for this purpose.

• Compensate losses
– Loss of water occurs in the distribution system due to faulty joints, broken pipes or water loss due to open taps, and due to unauthorized and illegal connections.
– Generally allowance of 15% of the total quantity of water is made to compensate for losses, thefts and wastage of water.

Water Demand

Therefore for average Indian conditions per capita water demand for a town is:
– Domestic

135 LPCD

– Industrial


– Public uses


– Fire Demand


– Losses


• Total

270 LPCD

Hence, total quantity of water for a city = 270 x population

It varies with population of the city and generally considered in the range of 150 to 270 LPCD.

Water Demand

Fluctuations in water Demand
– Per capita water demand varies from hour to hour, day to day and season to season.
– Seasonal fluctuation: Water demand will be more in summer and less in winter, except cold countries where taps are kept open not to allow freezing of ice. This seasonal variation may be 15 to 50%.

– Daily and hourly variation: Sunday and holiday more water consumption. Morning and evening hours more water consumption.

– The maximum daily consumption = 1.8 times annual average consumption – The maximum hourly consumption = 1.5 times average daily consumption.

– The variation in hourly demand is important for designing rate of pumping and determining capacity of reservoir.

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