Per capita demand of water is required for calculating the design period of the components of water supply system.
In this article, you will get to know what exactly is per capita demand of water, its formula and unit. Additionally, factors affecting the water demand are also discussed in detail.
What is Per Capita Demand of Water?
“The annual average amount of water needed by one person daily is the per capita demand of water.”
In simple terms, the water used by ONE person in ONE day is per capita water demand. However, average of water used by a person in one year is taken into consideration while deriving per capita demand.
Per capita demand is mostly denoted by “q”.
Per Capita Demand Formula
Per capita demand per day per head:
Unit of Per Capita Demand
The unit of per capita demand is liter/head/day.
Factors Affecting Per Capita Demand of Water
Per capita demand of water sees a huge variation across the globe. For India alone, the figure of per capita demand ranges from 100 to 360 litres/capita/day.
The variation in demand of water is due to many different factors as listed below:
- Population residing in the city
- Size of the city
- Climatic conditions of the city
- Economic class of the population residing in the city
- Industrial and commercial activities in the city
- Quality of supplied water
- Water pressure in the distribution system
- Development of sewerage facilities
- Water supply system
- Water cost
- Water charging method
1 Population
Per capita water demand varies directly with people. With increase in population, the water demand increases too.
The variations in per capita demand of water are tabulated below:
| S. No. | Population | Per Capita Demand |
| 1. | < 20,000 | 110 lit/head/day |
| 2. | 20,000-50,000 | 110-150 lit/head/day |
| 3. | 50,000-2 lakhs | 150-240 lit/head/day |
| 4. | 5 lakhs-10 lakhs | 275-335 lit/head/day |
| 5. | > 10 lakhs | 335-360 lit/head/day |
2. Size of the City
Larger the city, more is the per capita demand of water.
Increase in per capita demand of water with increase in size of the city has many reasons. Some of them are listed below:
- To maintain clean and healthy environment, more water is required in big cities as compared to small towns.
- More commercial and industrial activities are observed in cities. Hence, they require more water.
- More people in towns use air cooling than in population from smaller areas. This also increases the water demand.
- Affluent lifestyle also increases the water consumption.
As a matter of fact, size of the city does not directly affect the per capita demand of water. The type of area and the inhabiting people are deciding factors.
- A small area which is industrialized with huge water requirements will have higher water demand.
- Similarly, small town wherein affluent rich people are living will also have higher water demand.
3. Climatic Conditions
In extremely hot climates, the water consumption increases raising the water demand.
Increase in water demand in hot climates is due to:
- Longer bathing periods
- Frequent cleaning of homes with water
- Air cooling
- Water sprinkling in lawns/gardens/roofs
Now, water demand again has a probability to rise in freezing cold regions.
Increase in water demand in cold climates is due to:
- Habit of people to keep the taps running so as to avoid freezing of water in pipes.
- Higher possibility of water leakage from pipe joints as pipe metal remains in contact with cold.
4. Economic Class of Population
The per water demand varies according to the class of the population:.
- Affluent lifestyle of upper class communities of people increases the water demand.
- The slum dwellers consume the minimum amount of water.
Thus, we can say that the per capita demand directly varies with the economic class of the people.
5. Industrial and Commercial Activities
As the industrial and commercial activities propagate in an area, the water demand increases as per the requirement in the industry.
Some of the industries have huge water demand, which is several times higher than the domestic demand.
Industrial water demand does not depend upon the size or population of the city. But in general, more industries are established in big cities. Hence, we can say that they are also a contributing factor to the higher water demands in huge cities
6. Quality of Water Supplied
If the quality of water supplied is good, more water is consumed resulting into higher water demand. This is because alternate water sources are not required when the supplied water quality is good enough.
On the contrary, supply of poor quality water will make people use other sources of water like
- Private wells
- Hand pumps
- Ground water
7. Pressure in the Distribution System
More pressure in the water distribution system will result in more water consumption increasing the water demand. This is because:
- People residing in the upper storeys can use the water freely without any hassle.
- With increase in pressure, loss and leakage wastage are increased too.
Increasing the water head from 20 m to 30 m, increases the water losses by 20-30 %.
8. Development of Sewerage Facilities
The type of sewerage facility adopted by the city/town also affects the per capita water demand.
For instance, providing the city with flush system of latrines increases the water demand against the provision of the old conservative system.
9. System of Supply
The water may be supplied to the citizens in either of the following ways:
- Continuous supply of water: As indicated by its name, water is supplied 24 * 7 hours.
- Intermittent supply of water: Water is supplied only at peak periods of morning and evening. Or any other timing is adopted.
Ideally, the water consumption should decrease in intermittent water supply. However, it is not seen in real life.
The reasons for not seeing decrease in water demand in intermittent water supply system are:
- For the non-supply periods, the people store the water in tanks, drums, utensils, etc. When the fresh water is supplied again, the previously stored water is splashed away and fresh water is again stored. This increases wastage considerably.
- Some of the people keep the water taps open so that they can know water is supplied. Now, many times it may happen that the taps keep running for a long period when water supply is restored if the attendants are not aware.
10. Cost of Water
This is direct and self-understandable principle. Higher the cost of water, lesser will be its consumption.
11. Method of Levying Charges on Water
There are two methods generally adopted for levying the charges on water:
- Meter reading
- Flat rate (fixed charges irrespective of usage)
Flat Rate Water Charges:
As a fixed amount is to be paid irrespective off the usage, people generally do not practice economy while using the water. This leads to wastage and increased water consumption.
On the other hand, one of the greatest advantages is that the poor and low income group people can use the water freely. Levying water meters leads to very less consumption of water even on necessary usages by these people. This may result in unhygienic conditions.
Metered Charges:
The metered charges makes people use water in a considerable way reducing the water consumption.
Although the water consumption is reduced, unhygienic conditions may arise as discussed above.
Water meters again have the following limitations:
- Water meter hinders the flow of water resulting into pressure loss. This increases the water pumping cost.
- The cost of installation, maintenance, and reading of the water meters sums up to a high amount.
- Water meters are also liable to theft.
Hence, it is advisable to balance the cost of meter works against the cost of water conserved by meter installation.
Per Capita Demand of Water as per NBC
The per capita demand of water is mentioned in National Building Code of India, i.e., SP7 Part IX – Plumbing Services.
In SP7, Section 1 – Water Supply, Drainage, and Sanitation, water supply requirements are covered.
The per capita demand for water supply as per NBC (Clause 4.11) are tabulated below:
| Population | Per Capita Demand |
| > 20,000 (without flushing system) | |
| Supply through standpost | 40 lphd |
| Supply through house service connection | 70-100 lphd |
| 20,000-100,000 (with full flushing system) | 100-150 lphd |
| > 100,000 (with full flushing system) | 150-200 lphd (135 lphd for LIG* & EWS**) |
| lphd – litre per head per day *LIG – Low Income Group **EWS – Economically Weaker Section | |
How to Calculate Per Capita Demand of Water?
Per capita demand of water can be calculated in litre per head per day as follows:
- Total yearly demand of water is calculated first.
- Then the product of the design population of the city and 365 days.
- The yearly water demand is divided by the product of design population and 365.
In Short – Per Capita Demand of Water
Per Capita Demand: The water required in liters by one person in a day.
Per capita demand =
Unit: liter/head/day
Factors affecting per capita demand of water:
- Population residing in the city
- Size of the city
- Climatic conditions of the city
- Economic class of the population residing in the city
- Industrial and commercial activities in the city
- Quality of supplied water
- Water pressure in the distribution system
- Development of sewerage facilities
- Water supply system
- Water cost
- Water charging method