Per Capita Demand of Water
Per capita demand of water is the annual average amount of daily water required by one person and includes domestic use, industrial and commercial use, public use, wastes, thefts, etc. It may be expressed as
Whereas,
q is Per Capita Demand in litres per day per head
V is the total yearly water requirement of the city in a litre
Therefore, a city’s total annual water demand can be calculated using the above formula if the per capita demand is known or assumed. Per capita demand depends on a variety of factors (see below) and varies with consumer living conditions and the size and type of industries that have developed or may be developed in the region. For an average Indian city, as recommended by I.S. Code, per capita demand (q) can be assumed as in the following table.
| SL.No. | Use | Demand in l/h/d |
|---|---|---|
| 1. | Domestic Use | 200 |
| 2. | Industrial Use | 50 |
| 3. | Commercial Use | 20 |
| 4. | Civils or Public Use | 10 |
| 5. | Wastes & Thefts, etc | 55 |
| Total= | 335 per Capita Demand |
Multiplying this value of 335 litres/person/day by the projected population at the end of the planning period gives the city’s annual average daily water demand. Multiply this by 365 to get your annual water requirement in litres.
Factors Affecting Per Capita Demand
The average annual water demand (that is, per capita demand) varies greatly from city to city. This figure is generally 100-360 litres/person/day by Indian standards. These variations in total water use in different cities and communities depend on a variety of factors that need to be thoroughly investigated and analyzed before determining her per capita requirements for planning and design purposes. These factors are discussed below.
- Size of the City
- Climatic Conditions
- Types of Gentry and Habits of People
- Industrial and Commercial Activities
- Quality of Water Supplies
- Pressure in the Distribution System
- Development of Sewerage Facilities
- System of Supply
- Cost of Water
- The policy of Metering and Method of Charging
1. Size of the City
Larger cities generally have a higher per capita demand than smaller cities. Large cities require large amounts of water to maintain a clean and healthy environment. For example, large cities generally have canals running through them, so they need a lot of water (a house through a canal needs 4 to 5 times more water than a house without a canal). Similarly, large cities generally require more commercial and industrial activity and require more water. The wealthy and wealthy living in air-cooled homes can also increase city water use.
In fact, population indirectly affects the size of a city. Because even small cities can have high water consumption if they are fully industrialized or have industries that require huge amounts of water, or are inhabited by wealthy and wealthy people. On average, her per capita demand in Indian cities varies by population, as shown in the table below.
| Sl.No. | Population | Per Capita Demand in litres/day/person |
| 1. | Less than 20,000 | 110 |
| 2. | 20,000-50,000 | 110-150 |
| 3. | 50,000-200,000 | 150-240 |
| 4. | 200,000-500,000 | 240-275 |
| 5. | 500,000-1,000,000 | 275-335 |
| 6. | Over 1,000,000 | 335-350 |
Variations in Per Capita Demand with Population in India
*The figures shown here are liable to variation up to 25%.
2. Climatic Conditions
Water usage is generally higher in hotter, drier locations due to the increased need for bathing, cleaning, air coolers, air conditioners, lawns, gardens, roofs, etc. In colder countries, more water may be used because people keep taps open to prevent water pipes from freezing, and there may be more water leaking from pipe joints since metal contracts with cold.
3. Types of Gentry and Habits of People
Wealthier and upper-class communities generally use more water because their living standards are higher. Middle-class communities consume average amounts of water, while poor slum-dwellers consume very little. Thus, water consumption is directly dependent on the consumer’s economic status.
4. Industrial and Commercial Activities
The pressure of industrial and commercial activity in certain locations significantly increases water consumption. Many industries require very large amounts of water (much more than households need), which greatly increases the demand for water. As mentioned earlier, the demand for industrial water is not directly related to population or city size, but generally, there is more industries in big cities, increasing her per capita demand in big cities. However, for well-planned and zoned cities, estimating industrial and commercial needs separately can help predict water needs more accurately.
5. Quality of Water Supplies
If the water supply is of good quality and taste, people will consume more water and will not use other sources of water such as home wells or hand pumps. Similarly, certain industries such as boiler water supply that require standard quality water do not develop their own water sources and use public sources if the water supplied meets the required standards.
6. Pressure in the Distribution System
If the pressure in the distribution pipes is high and sufficient to make the water reach at 3rd or even 4th storey, water consumption shall definitely be more. This water consumption increases because of two reasons:
- People living in upper storeys will use water freely as compared to the case when water is available scarcely to them.
- The losses and wastes due to leakage are considerably increased if this pressure is high. For example, if the pressure increases from 20 m head of water, (i.e. 200 kN/m2) to 30 m head of water (i.e. 300 kN/m2), the losses may go up by 20% to 30%
7. Development of Sewerage Facilities
As pointed out earlier, the water consumption will be more, if the city is provided with a ‘flush system’ and shall be less if the old ‘conservation system’ of latrines is adopted.
8. System of Supply
Water may be supplied continuously for 24 hours a day or only during morning and evening peak hours. Supplying the water only during the peak hour (morning and evening) can lead to saving in water consumption due to losses occurring in a shorter time and consumers paying more attention to their water consumption. However, in many locations, intermittent delivery fails to provide greater savings than continuous delivery for the following reasons:
- In intermittent supply systems, water is generally stored by the consumer in tanks, barrels, utensils, etc. for the time it is not being supplied. This water, even if not used, is discarded when fresh supplies are restored. This greatly increases rejections and losses.
- People usually tend to leave the faucet open during off-hours so that they know when the supply is restored which leads to waste.
9. Cost of Water
Higher water prices can reduce the consumption of water. This may not be a big saving, as the rich and wealthy people are largely unaffected by such measures and policies.
10. Policy of Metering and Method of Charging
Water tax is generally charged in two different ways-
- On the basis of meter reading (meters fitted at the head of the individual house connections and recording the volume of water consumed).
- On the basis of a certain fixed monthly flat rate.
In the second case, i.e. when the delivery is not counted and the fee is fixed, people think that they only need to pay a fixed amount regardless of how much water they use, so generally doesn’t save water. Therefore, they generally consume water, and on multiple occasions, their taps are left unclosed. All this leads to a lot of waste and a lot of water consumption.
However, when the supplies are metered, people use only as much water as is required them. Although metered supplies are preferred because of lesser wastage. They generally lead to lesser water consumption by poor and low-income groups, leading to unhygienic conditions. Moreover, meters put unnecessary hindrances to the flow, resulting in loss of pressure and increased cost of pumping. Meters are also liable to be stolen and the cost of installing, repairing and reading the meters is generally high. In good water works management, it is, therefore, generally desired to work out the economics of metering and to balance the cost, of meterage against the value of water conserved by the reduction of wastages. At certain places, the saving in water due to meterage has really been large enough, as to permit postponing the otherwise needed extensions of supplies.
Also read:
- What is the difference between S-trap and P-Trap?
- What is Septic Tank? | Components | Uses
- Types of Water Demand
