The National Building Code (NBC) of India, 2016 provides detailed guidelines for estimating water supply requirements for residential buildings. Below is a summarized reference for calculating water tank size based on the population, type of dwelling, and water consumption:
Population Estimation per Dwelling Unit
- 1-bedroom dwelling unit: 4 persons
- 2-bedroom dwelling unit: 5 persons
- 3-bedroom dwelling unit: 6 persons
- 4-bedroom dwelling unit and above: 7 persons
- EWS dwelling unit: 4 persons
- Studio apartment: 2 persons
Water Requirement
- Domestic Needs: 70 to 100 liters per head per day (lphd) for urban communities.
- Non-domestic Needs (Flushing): Additional requirement based on the type of building occupancy.
- Total Requirements:
- Small communities (<20,000 population): 70–100 lphd.
- Medium communities (20,000–100,000 population): 100–135 lphd with a full flushing system.
- Large communities (>100,000 population): 150–200 lphd with a full flushing system.
- For MIG, LIG, and EWS categories: 135 lphd may be used instead of 150–200 lphd.
Example Calculation
For a 3-bedroom dwelling unit:
- Population: 6 persons
- Water consumption: Assume 135 lphd (domestic + non-domestic needs for medium population communities).
- Total Daily Requirement:
To calculate the water tank size, consider the following:
- Daily Requirement: Size the tank to store at least one day of water supply (810 liters for the example above).
- Buffer Storage: Add a buffer for emergencies or unforeseen demand.
Size of Under Ground Water tank in cuft
To calculate the size of a water tank in cubic feet (cuft), follow these steps:
- Convert Liters to Cubic Feet: 1 liter = 0.035315 cubic feet
Therefore, the volume in cubic feet (cuft) = Volume in liters × 0.035315. - Include a Buffer:
If a buffer of four days is needed, calculate the adjusted volume:
Adjusted volume = Daily requirement × (1+4).
Example Calculation:
Assume a 3-bedroom dwelling unit with a daily requirement of 810 liters and a four day buffer.
- Convert liters to cubic feet: 810 liters×0.035315=28.61 cuft.
- Add a 4 day buffer: 28.61 cuft×5=143.05 cuft. = 6ft X 6ft X 4ft
Result:
The under ground water tank size should be approximately 6ft X 6ft X 4ft for a 3-bedroom dwelling unit with a four day buffer.
Notes
- These figures are general guidelines and may vary depending on local water availability and conditions.
- For plotted developments, population estimation and tank sizing should consider the specific number and type of dwelling units.