What is Water Demand in Environmental Engineering | 6 Types of Water Demand | Factors Affecting Per Capita Demand4 min read

WATER SUPPLY:

Water is extremely useful to man, providing him luxuries and concerts, in addition to fulfilling his basic necessities of life. It has been estimated that two-thirds of the human body is constituted of water. Suitable systems should be designed for collecting, transporting, and treating water.

PUBLIC WATER SUPPLY SCHEME:

Essential elements.

  1. Intake and reservoir: To collect water.
  2. Water treatment plant: Screening, sedimentations, filtration, disinfection units, etc.
  3. Elevated tanks and standpipes: It provides storage to meet peak demands occurring for limited periods.
  4. Valves: It controls the flow of water m the pipe system.
  5. Hydrants: It provides a connection with the water in the main for fighting fires, flushing streets, etc.
  6. Distribution system: mains, sub mains, and branch lines that carry the water to the streets.
  7. Services: It carries the water to the individual house etc.

WATER DEMAND:

Water demand in environmental engineering is defined as the amount of water requested by users to meet their needs. In fact, the first requirement is to consider the demand, and the second requirement is to find sources to fulfill that demand.

Types of Water Demands:

  1. Domestic Water Demand
  2. Industrial Water Demand
  3. Institutional and Commercial Water Demand
  4. Demand For Public Uses
  5. Fire Demand
  6. Water is required to compensate losses in waste and thefts

1. Domestic Water Demand

  • As per is 1172-1983 as well as the National building code, the domestic consumption under normal conditions, an Indian city is expected to be around 135 liters/head/day.
  • Domestic water demand is around 55-60% of total water consumption.

Uses of Domestic Water: (table)

Uses Consumption in liters per capita per day
Drinking 5
Cooking 5
Bathing 55
Washing of clothes 20
Washing of utensils 10
Washing and cleaning of house and residence 10
Fleshing of latrines, etc 30
Total 135

2. Industrial water demand

The ordinary per capita consumption for industrial needs of a city is generally taken as 50 liters/capita/day.

3. Institutional and Commercial Water Demand

On average, per capita demand of 20 l/h/d is usually considered to be enough to meet such commercial and institutional water requirements, although this demand may be as high as 50 l/h/d for highly commercialized cities.

4. Demand For Public Uses

Demand for public uses is generally taken as 10 l/h/day.

5. Fire demand

Fire hydrants are usually fitted in the water mains at about 100 to 150 meters apart.

  • The per capita fire demand is thus generally ignored while computing the total per capita water requirement of a city.
  • Kilo liter of water required = 100√P

when population exceeding 50,000
where P = population in thousand.

The rate of fire demand is worked out on the basis of certain empirical formulas.

(A) Kuichling’s formula:

Q = 3182√P

where P = Population in thousand.

(B) Freeman’s formula:

  • Amount of water required in litres/min,

  • For a central congested high value city

Q = 4637 √P [1- 0.01 √P ]

6. Water is required to compensate losses in waste and thefts

  • In water supply, we also consider losses of water by leakage, wastes, thefts, etc.
  • Losses in waste and thefts we consider 55 lpcd

PER CAPITA DEMAND OF WATER

The total consumption of water for a water supply system in a year divided by the population and the number of days in the year is called per capita demand.

Per capita demand of water in Indian towns for various uses are:-

  • Domestic use = 135 liters/capita/day
  • Public use = 25 liters/capita/day
  • Industrial use = 40 liters/capita/day
  • Fire demand = 15 liters/capita/day
  • Losses, wastages and thefts = 55 liters/capita/day

That means the total demand is 270 liters/capita/day.

  • For an Indian city, as per the recommendation of IS. code, per capita demand, q = 270 l/h/d.

Factors Affecting Per Capita Demand:

  1. Size of the city
  2. Climate conditions
  3. Types of gentry and habits of people.
  4. Industrial and commercial activities.
  5. Quality of water supplies.
  6. Pressure in the distribution system.
  7. Development of sewerage facilities
  8. System of supply.
  9. Cost of water
  10. Policy of metering and Method of charging.

Variation in The Demand:

(1) Maximum Daily Consumptions:
= 180% of the annual average daily demand
= 1.8 x Average daily demand
= 1.8q

(2) Maximum Hourly Consumption

= 150 % of the average hourly demand of the month day.
2.7 x Annual average hourly demand

(3) Maximum Hourly Demand of Maximum Day

= 2.7 q

(4) Goodrich’s Formula

where P – % of the annual average draft for the time t in days.
t = time in days from 1/24 to 365

When t = 1 day (for daily variations), then
P = 180

∴ Maximum daily demand/Average daily demand = 180%

(5) The pipe mains carrying water from the source to the reservoir is designed for the maximum daily demand.
(6) Distribution system is designed for maximum hourly demand of 5.5
(7) The filters and other units of the treatment plant are designed for 2 times the average daily demand.
(8) Coincident Demand: The maximum daily demand when added to fire demands for working out total demand is known as coincident demand.

WATER SUPPLY SCHEMES:

water supply schemes
water supply schemes

• In case of dams and reservoirs—Generally no need for pumps.
• In case a river is used as a source, is required dumping equipment is required

DESIGN PERIODS:

  • The future period or the number of years for which a provision is made in designing the capacities of the various components of the water supply scheme is known as the design period.
  • Water supply projects, under normal circumstances, may be designed for a design period of 30 years. These 30 year is to be counted after the completion of the project.

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