Water Demand in Water Supply System

Water demand means the requirement of water by any individual or by any sector to fulfill their water needs. It is normally expressed as litres per person per day or LPCD. For the planning of water supply system, estimation of water demand is the key parameter. In India, more than 80% of the total water potential created in our country is consumed by agriculture sector. The remaining portion is utilized to meet domestic, industrial and other demands.

As we know that India is a developing country. So the improvement in lifestyle and associated industrial development push up the per capita demand for water.

The prediction of accurate quantity of water demanded by the public is very difficult, because there are many variables factors affecting water consumption but there are some certain thumb rules and empirical formulas, which are used to assess the water demand and fairly give accurate results.

There are different types of water demands:

1. Domestic water demand

The demand which includes the water required in private building for drinking, cooking, bathing, washing, gardening purposes etc. which may vary according to the living conditions of the consumers is known as Domestic water demand.

The total domestic water consumption is between 135 to 225 l/h/d.

As per IS code, the minimum domestic water demand under normal conditions for a twon with the full flushing system should be taken as 200 l/h/d although it can be minimized upto 135 l/h/d for economically weaker section and low income group sections depending upon prevailing conditions.

2. Industrial water demand

The water demand required for the pre-existed or likely to be started in future industries, in the city for which water supply is being planned is known as industrial water demand. This type of water demand thus vary with the types and number of the industries present in the town/city.

In industrial cities, the per capita requirement may finally be computes to be as high as 450 l/h/d as compared to the normal industrial requirement of 50 l/h/d.

Water requirements for commercial buildings as per IS code
Water requirements for commercial buildings as per IS code
water demand
Water required by certain important industries
3. Institutional and Commercial Water Demand

On an average, a per capita demand of 20 l/h/d is usually considered to be enough to meet of such commercial and institutional requirements although of course, this demand may be as high as 50 l/h/d for highly commercial cities.

industrial water demand
Institutional and commercial water demand as per individual requirement
4. Demand for Public Uses

Water requirements for washing the roads, gardening, parks etc. are included in demand for public. A nominal amount, not more than 5% of the total consumption may be provided to meet this demand. A figure of 10 lpcd is usually added on this account while computing toal water requirements.

5. Fire Demand

As we know that some water is also required by fire department of a city to counter the accidents. For this purpose, fire water requirement is also considered in calculation. The quantity of water required as a fire demand is very less. For a total amount of water consumption for a city of 50 lakhs population, it only amounts to 1 lpcd of fire demand. But this water should be easily available and always kept stored in storage reservoirs, as quantity of water required is in very less duration.

In dense areas or populated areas, fire generally breakout and may lead to serious damages, if not controlled effectively. Therefore big cities generally maintain full firefighting squads. A provision should, therefore be made in modern public water scheme for fighting fire breakouts.

To meet the fire demand, following requirements must be met

  • The minimum water pressure available at fire hydrants should be of the order of 100 to 150 KN/m2 (10 to 15 m of water head) and should be maintained for 4 to 5 hours of constant use of fire hydrant.
  • The jet streams are simultaneously thrown from each hydrands: one on the burning property and one each on the adjacent property on either side of the burning property. The discharge of each stream should be about 1100 l/min9hello2143
  • The number of fire jets required depend on the size of population and given by “F = 2.8 under root P”, where P = Population in thousands.
  • Generally, for a city of 50 lakh population, the fire demand is 1 lpcd.
6. Water losses demand

Water loss demand or waste water demand includes the water lost in leakage due to bad plumbing or damaged meters, stolen water due to unauthorized water connections and other losses and wastes. These loses should be taken into account while estimating the total requirements. Even in the best managed water works, this amount may be as high as 15% of the total consumption which is nearly 55 lpcd.

Total Maximum Water Demand

It is the sum of above six demands and IS code permits for India, total maximum demand of 335 lpcd.

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