L1 - Introduction.ppt

WATER SUPPLY ENGINEERING
ENVIRONMENT ENGINEERING I
INTRODUCTION TO WATER SUPPLY ENGINEERING
QUANTITY OF WATER

Municipal Water Supply Systems
Central Objective: To ensure supply of safe quality and adequate quantity of water to end users.
Needs to Explore:
◦ Water Demand – How much water to extract from source?
◦ Water Source – What are the sources available?
◦ Water Intake – How to withdraw water from the source?
◦ Water Quality – What treatments are required?
◦ Spread of the users – Where to distribute and how to distribute?
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ASST. PROF. PRACHI DESSAI

Water Demand
1. Daily needs at homes
2. Institutions/business/parks/markets areas
3. Watering of public parks or gardens, public
fountains, sprinkling and road washing,
cleaning public sanitary blocks etc. for civic
and public uses.
4. Industries & Commercial establishments.
5. Fire fighting.
6. Compensate for water losses.
3

Need for Estimating Water Demand
Water services are usually designed in advance for future.
The kind of infrastructure and set-up needed (pumping power, reservoir capacity, pipe sizes,
treatment plant capacity etc.) will depend on water demand to be fulfilled.
Under-estimation leads to inadequate design whereas over-estimation results in uneconomical
and inefficient water supply system.
Therefore, it is important to estimate the water demand to the best accuracy possible for the life
period of the water supply projects.
4

Types of Water Demand for a Town/City
Domestic Water Demand:
Houses - Drinking, cooking, bathing, laundry,
cleaning utensils and floors, toilet flushing and
gardening.
◦ The amount depends on the living conditions
of the consumers.
◦ As per IS: 1172-1963 - 135 litres/day/capita.
◦ Developed countries this figure may be 350
litres/day/capita because of use of air
coolers, air conditioners, maintenance of
lawns, automatic household appliances.
Details of the domestic consumption are
Drinking 5 litres
Cooking 5 litres
Bathing 55 litres
Clothes washing 20 litres
Utensils washing 10 litres
House washing 10 litres
Total 135 litres/day/capita
5

Commercial and Industrial Water Demand:
Offices, hospitals, hotels, restaurants, cinemas,
schools, etc., and factories or industries.
◦ Varies - Nature of the town or city and with
the number and types of establishments and
factories/industries.
◦ The quantity of water demand for industrial
purpose is around 20 to 25% of the total
demand of the city.
◦ Commercial – 15 l/head/day
◦ Industry – 40 to 500 l/head/d
6

Types of Water
Demand for a
Town/City
Demand for Civic or Public Use:
Includes water required for watering of
public parks/gardens, supply to public
fountains, road sprinkling and washing,
cleaning public sanitary blocks and
markets etc.
As per IS:1172-1963, water supply
requirements for the public buildings
other than residences as follows.
7

Demand for Public use:
Washing and sprinkling on roads, cleaning of sewers, watering of public parks, gardens, public
fountains etc. comes under public demand.
Provision of 5% of the total consumption is made designing the water works for a city.
8

Fire Demand:
Water required for fire-fighting emergency purposes.
9

Compensating Water Losses: 15% of total
quantity of water is made to compensate for losses,
thefts and wastage of water
The following are the reasons
Defective pipe joints, cracked and broken pipes,
faulty valves and fittings.
Consumers keep open their taps of public taps even
when they are not using the water and allow the
continuous wastage of water
Unauthorized and illegal connections
10

Estimation of Municipal Water Demand
Quantity of water required for municipal activities depends on:
A. Consumption rate (Per capita demand in litres/day/head).
B. Total population to be served (at the end of design period).
Quantity Required = Per capita demand x Total Population
Additional demands such as Fire-fighting, Institutional and Industrial needs, losses etc.) is added.
Water requirements are never constant, thus fluctuations and variations in water demand must be
given due consideration
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PER CAPITA DEMAND
If ‘Q’ is the total quantity of water required by various purposes by a town per year and ‘p’ is
population of town, then per capita demand will be
Depends on various factors like standard of living, no. and type of commercial places in a town etc.
For an average Indian town, the requirement of water in various uses is as under
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PER CAPITA DEMAND
USE CONSUMPTION (LPCD)
Domestic 135
Industrial use 50
Commercial use 20
Civic or public use 10
Waste, Theft, Losses 55
Total 270 lpcd
E.g. Consider a city having a population of
10,000. The per capita demand of the city is 270
LPCD. Calculate the total Quantity of water
required.
Soln.
Quantity Required = Per capita demand x Total Population
= 270 L/h/d X 10,000 h
= 27,00,000 L/day
13

Factors Affecting per Capita Demand
1. Size of the city
2. Presence of industries
3. Climatic conditions
4. Habits of people
5. Economic status of the people
6. Quality of water
7. Hours of supply
8. Pressure in the distribution system
9. Efficiency of water works administration
10. Cost of water
11. Policy of metering and charging method
14

Fluctuations in Water Demand
If this average demand is supplied at all the
times, it will not be sufficient to meet the
fluctuations in the water demand, which could be
due to:
◦ Seasonal or Monthly Variation
◦ Daily Variation
◦ Hourly Variation
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Fluctuations in Water Demand: Seasonal
or Monthly Variation
In India, Rate of Water Consumption
During summers - 30-40 % higher than the annual average
During winters - 20 % lower than the annual average as less requirement of water for domestic
uses.
[In some of the higher-economy countries like Australia, the domestic water demand in winter is
higher than summer because more water used in getting hot water for bathing, cleaning etc.]
During rainy season, the outdoor demand of water for gardening etc. is much less.
16

Fluctuations in Water Demand: Daily
Variation
Depends on day-to-day individual activities and climatic conditions.
Water consumption increases during weekends, holidays and festival days (Holi).
The requirement is lower on the days of rain.
In India, the maximum daily demand of water is generally taken as 180 % of the annual average
daily demand of water. [Peak factor = 1.8]
Peak factor may vary in different design calculations
17

Fluctuations in Water Demand: Hourly
Variation
Certain hours of the day, water demand is found to be very high.
Generally, morning hours 6:00-10:00 AM and evening hours 6:00-9:00 PM the water
consumption is higher than average hourly consumption. During other hours the requirement is
very less.
The maximum hourly demand of water is generally taken as 150 per cent of the average hourly
demand on the day of maximum use of water (or the maximum day for the year).
[Hourly Peak factor = 1.5]
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Fluctuations in Water Demand: Hourly
Variation
Maximum daily demand = 1.8 x average daily demand
Maximum hourly demand of maximum day i.e. Peak demand
= 1.5 x average hourly demand
= 1.5 x Maximum daily demand/24
= 1.5 x (1.8 x average daily demand)/24
= 2.7 x average daily demand/24
= 2.7 x annual average hourly demand
19

Design Population
The design of water supply schemes are based on the projected population of a particular area,
estimated for the design period.
Any underestimated value will make the system inadequate for the intended purpose while
overestimation will make it costly.
As over the years the population of the area is ever changing, the system should be designed by
considering of the population at the end of the design period, or end of the first phase duration
(before next phase extension is likely to be implemented).
After collecting the present and past population record for the area (from census population
records), the population at the end of design period can be predicted using various methods by
considering the growth pattern of the concerned area.
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Population Forecasting Methods
Arithmetic Increase Method
Geometric Increase Method
Incremental Increase Method
Logistic Curve Method
Growth Composition Analysis Method
Master Plan Method
Decreasing Rate of Growth Method
Simple Graphical Method
Comparative Graphical Method
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Concept of Design Period
The complete water supply project includes
huge and costly constructions such as dams,
reservoirs, treatment works and network of
distribution pipelines.
While designing and constructing these works,
they should have sufficient capacity to meet
future demand of the town for number of years.
The number of years for which the designs of
the water works have been done is known as
design period.
Mostly water works are designed for design
period of 22-30 years, which is fairly good
period.
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Recommended Readings
i. Mark J. Hammer; Water and Waste Water Technology; Prentice Hall of India.
ii. S. K. Garg; Water Supply Engineering; Khanna Publ.
iii. B. C. Punmia, A. K. Jain; Water Supply Engineering; Laxmi Publication.
iv. G. S. Birdie; Water Supply Engineering and Sanitary Engineering; Dhanpat Rai.
v. R. C. Rangwala; Water Supply Engineering, Charotar Publ. House.
ASST. PROF. PRACHI DESSAI 23

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