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Chapter: Environmental Engineering - Demand For Water

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Various types of water demand

Which planning a water supply scheme, it is necessary to find out not only the total yearly water demand but also to assess the required average rates of flow (or draft) and the variations in these rates. The following quantities are therefore, generally assessed and recorded.

DEMAND FOR WATER

 

VARIOUS TYPES OF WATER DEMAND

 

Which planning a water supply scheme, it is necessary to find out not only the total yearly water demand but also to assess the required average rates of flow (or draft) and the variations in these rates. The following quantities are therefore, generally assessed and recorded.

 

i)                   Total annual volume (V) in liters or million liters.

ii)                Annual average rate of draft in liters per day, i.e V/365

 

iii)              Annual average rate of draft in liters per day per person i.eliters per capita per day or lpcd called PER CAPITA DEMAND (q) or RATE OF DEMAND.

 

iv)

Average rate of draft in liters per day per service i.e

V

×

1

365

No of services

 

 

 

 

v)                Fluctuations in flows expressed in terms of percentage ratios of maximum or minimum yearly, monthly, daily or hourly rates to their corresponding average values.

 

It is difficult to precisely assess the quantity of water demanded by the public, since there are many variable factors affecting water consumption certain thumb rules and empirical formulas are therefore generally used to assess this quantity, which may give fairly accurate results. The use of a particular method or a formula for a particular case has therefore, to be decided by the intelligence and fore sightedness of the designer. The various types of water demands, which a city may have, may be divided into the following classes.

 

i)                   Domestic water demand

ii)                Industrial and commercial water demand

iii)              Demand for public uses

iv)              Fire demand

v)                Water required compensating losses in wastes and thefts.

 

As correctly as possible the total water demand of a particular section of the community, all these demands must be considered and suitable provision made depending upon the needs of those people for whom the water supply scheme is to be designed.

 

DOMESTIC WATER DEMAND: This includes the water required in private buildings for

 

drinking, cooking, bathing, lawn sprinkling, Gardening, sanitary purposes etc….

 

This amount varies according to the living conditions of the consumers on an average this domestic consumption under normal conditions in a Indian city is expected to be around 135 litres /day/person as per Id:1172,1971. The total domestic consumption generally amounts to 50-60% of the total water consumption.

AVERAGE DOMESTIC WATER CONSUMPTION IN A INDIAN CITY

USE  CONSUMPTION IN LPCD

Drinking     5

cooking       5

Bathing       55

Washing of clothes        20

Washing of utensils       10

Washing  and  clearing  of  houses    10

and residences     

          30

TOTAL       135 lpcd

 

 

 

INDUSTRIAL AND COMMERCIAL WATER DEMAND

 

This includes the quantity of water required to be supplied to offices, Factories, different industries, hospitals, hostels, etc…. This will vary considerably with the nature of the city and with the number and types of industries and commercial establishment there is no direct relation of this consumption with the population and hence the actual requirements for all industries should be estimated. The water requirements for buildings other than residences as per is standards are as follows.

 

 

Type of building   Age  consumption lpcd

          1.Factories  45

           a) where bathrooms are required to be provided

           b) where no bathrooms are required          to be provided      30

          2.Hospitals (including laundry) per bed    

           a) Number of beds < 100        340

           b) Number of beds > 100       450

          3.Nurse homes and medical quarters          135

          4.Hostels    135

          5.Hotels (Per bed) 180

          6.Restauvants (Per seat) 70

          7.offices      45

          8.Cinemas,  Auditoriums  and  theatres (per seat) 15

          9.Schools   

           a) Day schools    45

           b) Residential school     135

DEMAND FOR PUBLIC USES (MUNICIPAL CONSUMPTION)

 

This includes the quantity of water required for public parks, gardening, washing and sprinkling on roads, use in public fountains etc…..

 

A nominal amount not exceeding 5% of the total consumption may be added to meet this demand on an arbitrary basis or else the consumption of water for municipal purposes as given below may be considered.

 

PURPOSE WATER CONSUMPTION

         

Public parks         1.4 litres/m2/day

         

Road watering      1-1.5 litres/m2/day

         

Sewer cleaning     4.5 litres/head/day

 

Extinguishing for is very small in a year but the rate of consumption is large. The scheme should provide the necessary peat demand of water for firefighting (although fire hydrants with separate water mains at about 100-150m apart are provided) The water requirements for extinguishing fire depends on bulk, congestion and fire resistance of buildings. Indirectly we can say, it ,mainly depends on the population. The minimum limit of fire demand is the amount and rate of supply that are required to extinguish the largest probable fire that may occur in a town.

 

Which designing public water supply schemes the rate of fire demand is sometimes treated as a function of population and is worked out on basis of certain empirical formulas which are as follows.

 

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