Water
Demand and its Variation
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Water
demand
Water is a prime necessity for life
and that has led to growth of population along the banks of natural water
courses and springs. The water required for various purposes as domestic, livestock,
institutional and commercial, fire fighting, industrial, municipal or public,
losses or wastage demand are the types of water demand. The amount of water required
for a rural/urban community depends on factors like the economic level of
community, their consciousness and other physical and social aspects. This
various demand is not essential to take in account to calculate total water
demand of city or community or town so that firefighting, municipal, industrial
demand may be excluded in rural areas where as livestock demand is excluded in urban
area.
1. Domestic Water
demand:
This includes the water which is
required for use in private residence for drinking, cooking, and bathing,
washing of cloths, lawn watering and gardening and sanitary purpose. The amount
of domestic water demand depends on the living conditions of the consumers, · climatic
condition, habit, social status etc. The design of gravity flow community water
supply schemes in Nepal, in the past has taken 45 lpcd as per the
recommendation of the WHO. The provision of 45lpcd is considered to include
allowances for drinking and cooking, personal washing, wastage and leakage, and
some portion of the domestic animal demands.
Generally adopted per capita
domestic needs are as follows: –
2 Livestock Water
demand:
The quantity of water required for
domestic animals is called livestock demand. Livestock is an important
component of the life style in rural Nepal. It has utilizes both as draft animals
for tilling land and a source of income. The water consumption by the livestock
(animals) must be known specially for farms and livestock areas. The
approximate consumption given below:-
Big animal (Cowl buffalo/horse) 45
lit/animal
Small animal(Goat, dog, rabbit
etc.) 20 lit/animal
Poultry(Birds, chicken, duck etc.)
0.2 lit/birds
3 Commercial /Institutional demand Water
demand:
It includes the demand for commercial
establishments and institutions like universities, school, cinema hall, office
building, warehouse, stores, hotels, hospitals theaters, clubs etc.
Institutional demand refers to the water needed for offices, schools and health
posts, in the community. In some case, tourist resorts, local industries may
also have to be supplied water from the scheme. Government institutions
deriving service from the water scheme must also support the water user
committee (WUC) in operating and maintenance the schemes. In community water
supply scheme priority should be given to supply water to
schools and health posts. The
following institutional water demand should be adopted:-
4. Public/Municipal Water
demand:
Water required for public or
municipal utility such as washing and sprinkling on road, flushing sewers,
watering public parks . etc. is municipal or public demand. A provision of 5 to
10% of the total demand is taken as this demand. This demand is only considered
in urban water supply system.
5. Industrial demand Water
demand:
Industrial area could be located
far from the city though it may locate in periphery of city which may be vital
in calculating water demand. Normally 20-25% of total demand is taken for
industrial demand. It is considered only in urban area and depends upon the
type and size of industry.
6. Fire fighting Water
demand:
Fire is generally break in thickly
populated localities and the industrial area and causes serious damages of
properties. During outbreak of fire, the water is used for firefighting is called
fire demand. This demand is not fixed so it is difficult to calculate demand.
Different empirical formula can be used to determine fire demand but it cannot
directly used for community context. This demand is considered in urban water
supply system.
The quantity of water required for
fire fighting is calculated by following formula
If Q= water required in l/min and
P= population in thousands then.
(a) According to National board of
fire
Q = 4637 ÖP (1-0.01 ÖP )
Where Q=quantity in lit/sec
P
= population in thousands
(b) According to Freeman’s formula
Q = 1136.50(P/5 + 10)
Where Q=quantity in lit/sec
P = population in
thousands
(c) Kuichling’s formula,
Q = 3182 ÖP
Where Q=quantity in lit/sec
P = population in
thousands
(d) Buston’s formula
Q = 5663 ÖP
Where Q=quantity in lit/sec
P = population in
thousands
(e) Indian water supply manual
(1976) formula:
Q = 100 ÖP where Q in m3/day
Where Q=quantity in lit/sec
P = population in
thousands
7. Loss and wastage
Loss and wastage may be termed as unaccounted
for water which includes
water due to faulty valves and
fittings, poor distribution system, defective pipes, unauthorized
connections, tap open etc. Lost and
wasted being uncertain it cannot be predicted precisely so
generally it is taken as 15 to 20%
of total demand.
Causes of loose and wastage of
water.
* Leakage and over flow
reservoir.
* Leakage from main and
service pipe connections.
* Leakage and looses
from consumers premises.
* Wastage for public
taps.
8. Total water demand
The sum of all water demands is
total water demand as given below.
TD=DD+LD+ID+ID+PD+FD+LD
Where,
TD = Total water demand
DD = Domestic water
demand
LD = livestock demand
ID = institutional and
commercial demand
ID = Industrial demand
PD = Public/municipal
demand
FD = fire demand
LD = Losses and wastage
demand
9. Per capita Water
demand:
It represents the average
consumption or demand of water per day for various purposes including all
demand of water for person. It is expressed as Lpcd/Lphd.
Let ‘Q’ be the total quantity of
water required per year in liters by city or town having population (P), and
per capita demand or rate of water demand (q) usually expressed in lpcd is given
by the following expression .
Water
demand variation.
The
rate of demand of water represents the average consumption or demand of water
per capita/head per day. Rate of demand does not remain constant but varies
with the season or month of the year, with the days of week, and with the hours
of the day. These variations in the rate of demand of water are termed as,
i)
Seasonal
variations
The rate of demand of water varies
considerably from season to season. In summer water demands usually 30 to 40%
above the annual average rate of flow of water, because more water is required
for drinking, bathing, washing etc. In winter the average rate of demand is
about 20% lower than the annual average rate of demand of water because of less
requirement of water.
Qseasonal = 1.3 X Qaverage
(In India)
ii)
Daily
variations
Due
to change in the day to day climatic conditions, or due to the day being a
holiday or some
festivals
day the rate of demand of water varies from day to day and called daily
variations.
Qdaily = 1.8 X Qaverage
(In India)
