WATER DEMAND

LECTURE 3

WATER DEMAND

• Drinking water must be wholesome (free from toxic chemicals, pathogens) and palatable (aesthetic- free from turbidity, color, odour etc.)

• Any disease will have a source, a causative agent, a vehicle fortransmission and a receiver. The vehicle may be air, water, orpersonal contact. The agent could be a bacteria, virus orprotozoa. The turbidity in water generally shields thepathogens.

• Ground water though comparatively free from pathogens contain minerals or dissolved salts such as nitrates, lead, iron, sulphates, carbonates, etc.

CONSUMPTION OF WATER

• Domestic• Industrial• Municipal• Commercial• Fire fighting• Live stock• Leakages

DOMESTIC WATER DEMAND

This includes the water required in private buildings for drinking, cooking, bathing, lawn sprinkling, gardening, sanitary purposes, etc.

Amount of domestic water consumption per person shall vary according to the living condition of the consumers.

IS code infact lays down a limit on domestic water consumption between 135-225 l/h/d.

In a developed and effluent country like U.S.A ., usually goes as high as 340l/h/d.

Total domestic water consumption usually amounts to 50-60% of the total water consumption.

Domestic (Indian)a). Population upto 10,000(rural) ------------- 70 -100

lpcdb). Population 10,000 – 50,000(semi- urban) ------- 100 -500

lpcdc). Population above 50,000(urban) ---------------- 250 - 400

lpcd

MINIMUM DOMESTIC WATER CONSUMPTION (ANNUAL AVERAGE )

USE INDIAN TOWNS AND CITIES WITH FULL FLUSHING SYSTEMS AS PER IS1172-1993

WEAKER SECTION AND LIG COLONIES IN SMALL INDIAN CITIES AND TOWNS

CONSUMPTION IN LITRES PER HEAD PER DAY (l/h/d)

Drinking 5 5

Cooking 5 5

Bathing 75 55

Washing of clothes 25 20

Washing of utensils 15 10

Wahing and cleaning of residences

15 10

Lawn watering and gardening

15 -

Flushing of water etc.

45 30

Total 200 135

INDUSTRY UNIT WATER KL/ UNIT

Automobiles Vehicle 40distillery (alcohol) Kilolitre 122-170

Fertilizer Tonne 60-200Leather (tanned) Tonne 40

paper Tonne 200-400Steel Tonne 200-250Sugar Tonne 1-2Textile Tonne (goods) 90-140

Petroleum refinery Tonne(crude) 1-2

The industrial water demand varies with the number and type of industries in the city .

Industrial cities ,per capita water requirement may be as high as 450 l/person/day as

compared to the normal industrial requirements of 50 l/person/day.

INDUSTRIAL WATER REQUIREMENTS

INSTITUTIONAL AND COMMERICAL WATER DEMAND

The water requirement of institutions such as hospitals, hotels, restaurants, schools, colleges, railway stations, offices, factories, etc.

On an average, a per capita demand of 20l/head/day is usually considered to be enough to meet such commerical and institutional water requirements.

Type of institutional or commerical establishment

Average water consumptionin l/head/day

Offices 45-90

Hospitals 450(per bed)

Hostels 135

Schools 45-90

Restaurants 70 l/seat

Factories 45l/seat

Theatres 15l/seat

FIRE FIGHTING

Fire fighting requires sufficient quantity of water, so as to throw it over the fire at

high speeds . The quantity of water required extinguishing fires should be easily

available and kept always stored in storage reservoirs.

Fire hydrants are usually fitted in the water mains at about 100 to 150m apart and

firefighting pumps are immediately connected into them by fire birgade personnel.

These pumps throw water at high pressure in the order of 100-150kN/m^2.

High rate of water consumption during a fire considerably affects the design of

distribution system ,hence while designing public water supply schemes, the rate of

fire demand is sometimes treated as function of population .

contd..

It is worked out on the basis of certain empirical formulas, as follows

1).Kuichling”s formula Q = 3180 √ P

where Q=AMOUNT OF WATER REQUIRED IN L/MIN

P = POPULATION IN THOUSANDS

2). Freeman formula Q = 1136 [ P/5+10]

F = 2.8 √ P ; where F = number of simultaneous fire streams

3). National board of fire under writers formula Q = 4637√ P [1-0.01 √ P ]

4). Buston formula Q = 5663√ P

VARIATION IN DEMAND and their effects on the design of various components of a water supply scheme.

Maximum daily demand = 1.8*Average daily demand

Maximum hourly demand = 1.5* Average hourly demand of a maximum daily demand

= 2.7* Average hourly demand

DESIGN PERIOD : a reasonable future period for which provision is made in water supply scheme.

It shall not be too large or too short. A design period of 20-30 yrs is generally adopted.

Depends on useful life of component, difficulty in future expansion, funds available, anticipated rate of population growth, interest rate etc.

COMPONENT DESIGN PERIOD Dams 50 Years

Conveying Main Pipes 30 Years

Distribution System 30 Years

Water Treatment Units 15 Years

Pumps, Service Reservoir 15 Years

FACTORS AFFECTING CONSUMPTION

• Climatic conditions• Habits of people• Age of pipes• Sewerage system • Metering• Intermittent or continuous supply• Industrialization

LEAKAGES

• Depends upon the age of the pipes. It may vary from 10% to as high as 50%

• Live Stock:• Horses ------- 45 liters/animal/day• Cows ------- 70 liters/animal/day• Dogs ------- 20 liters/animal/day• Sheep ------- 15 liters/animal/day• Municipal:• Public Parks ------- 1.5 liters/sqm/day• Street Cleaning------ 4 to 5 lpcd