The quantity of water required by a community, society or industry is called water demand. It is normally expressed as litres per person per day or LPCD. While designing the water supply scheme for a region, it is necessary to determine the total quantity of water required for different purposes. The various types of water demands are:
Industrial or commercial water demand refers to requirements of water to commercial buildings or centres like office buildings, warehouses, stores, hotels shopping centres, health centres, schools, temples, cinema houses, railway and bus stations. The water demand in such cases is 45 litres/day/capita. Universities, commercial buildings and centers including office buildings, warehouses, stores, hotels, shopping centers, health centers, places of worship, cinema houses, railways and bus stations fall under this category. Indian standard; IS1172:1963 sets water supply requirements for public buildings other than residences varying from 45 to 450 LPCD.
Quantity of water required for public utility purposes like washing and sprinkling on roads, watering of public parks, gardens, etc comes under public demand and 5% of the total consumption is set aside while designing water works for a city.
The quantity of water to be set aside for fire fighting is calculated by different formulae as listed below:
The following are the reasons for losses and wastage:
- Domestic water demand
- Industrial or commercial water demand
- Fire demand
- Demand for public uses
- Compensate losses demand
Industrial or commercial water demand refers to requirements of water to commercial buildings or centres like office buildings, warehouses, stores, hotels shopping centres, health centres, schools, temples, cinema houses, railway and bus stations. The water demand in such cases is 45 litres/day/capita. Universities, commercial buildings and centers including office buildings, warehouses, stores, hotels, shopping centers, health centers, places of worship, cinema houses, railways and bus stations fall under this category. Indian standard; IS1172:1963 sets water supply requirements for public buildings other than residences varying from 45 to 450 LPCD.
Quantity of water required for public utility purposes like washing and sprinkling on roads, watering of public parks, gardens, etc comes under public demand and 5% of the total consumption is set aside while designing water works for a city.
The quantity of water to be set aside for fire fighting is calculated by different formulae as listed below:
KUICHLING's FORMULA (This formula is best suited for Indian conditions)
BUSTON's FORMULA
FREEMAN's FORMULA
Where P is population in thousands
The following are the reasons for losses and wastage:
- Defective pipe joints, cracked and broken pipes, faulty vaulves and fittings
- Wastage by consumers
- Unauthorised and illegal connections
Per capita demand = Total yearly requirement of city in litres / (365 * Design population)
Average per capita demand = 335 litres / hour / day
Domestic demand = 200
Industrial demand = 50
Commercial demand = 20
Public use = 10
Losses and theft = 55
TOTAL = 335
Factors affecting per capita demand
- Size of a city
- Climatic conditions
- Demography and habits of people
- Industrial and commercial activities
- Quality of water supply
- Pressure in distribution system
- Sewerage facilities
- System of supply
- Cost of water
- Policy of metering and method of charging
Factors affecting losses and wastes
- Water tight joints
- Pressure in distribution system
- System of supply
- Metering
- Unauthorised connections
Variations in demand
- Daily consumption
- Seasonal variation
Maximum daily consumption = 1.8 * Average daily demand
Environmental engineering
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