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.
Average rate of draft in liters per day per service i.e
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
Washing of clothes 20
Washing of utensils 10
Washing and clearing of houses 10
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
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
5.Hotels (Per bed) 180
6.Restauvants (Per seat) 70
8.Cinemas, Auditoriums and theatres (per seat) 15
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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