How to Calculate Underground Water Tank Capacity for Residence?

In the case of residential buildings, this is very necessary to construct an underground water tank. Without the construction of an underground water tank, the house is not complete in the present situation. In the new construction house, the underground water tank is compulsory to fulfill the water needs.

Today we will discuss how to estimate underground water tank capacity and the sizes. This calculation will be calculated for the 8-person and the average water requirement per day is 150 liters.

The Water tank capacity depends on the type of building and the number of people living in such a building.

We have calculated based on the given data. That is 8-person and the Average water requirement per person is 150 liters per day.

Calculate Water Tank capacity requirements

  • Calculate daily water usage
  • Consider peak usage times
  • Account for future growth
  • Factor in reserve capacity for emergencies
  • Evaluate local regulations and standards
  • overhead and underground water tank capacity calculation is necessary
  • Calculate the oversized capacity tank as compared to the required capacity
  • manage construction cost
Note: Tank capacity should be designed for average water requirements.

The key point of a Large underground Water tank

Leftover water accumulates, leading to contamination.

Old water mixes with new, posing health risks.

Regular maintenance is necessary, especially with large tanks.

Underground tanks require frequent cleaning, necessitating hired help.

If you are designed with oversized tank capacity compared to average these above points are a little bit disadvantaged. so that Calculate the Underground Water Tank Capacity as an average requirement.

Let’s jump to the calculation part

Calculate Water Tank Capacity(Formula)

The following calculation is just for example. This is not your exact calculation for your needs. If you are designing a water tank for 8 people with 150 liters per day, this is helpful to you. Otherwise, I am not sure which capacity you require.


Number of People: 8 Person

Water required per person: 150 liters per person/day

Total Water Require=Number of people x minimum water required per person per day
Total Water Require=8 x 150=1200 liters

Total water Require volume= 1.2 cub meters (1 cub meter=1000 liters)

Now Calculate the volume of Water requirements

Calculation of Underground Water tank size


Shape of water tank= Rectangular

Depth of Water tank 1.5 meters

we have a formula for Volume

Volume= Area x Height


Area=1.2/1.5=0.8 m2 (square meter)

Area of Rectangular= Length x Breath

Assuming L=2B

0.8 m2=2B x B



B=√0.4=0.63 meter

So the Total Length L= 2B=2*0.63= 1.26 Meter


Number of People is 8
The minimum water required per person per day is 150 Liters
Rectangular shape water tank
The height of the Water tank is 1.5 meters
The length of the Water tank is 1.26 Meters
The breath of the water tank is 0.63 meters
The area of the water tank is 0.8 m2

Sample Estimate for underground water tank

Renovation Works: Underground Water Tank
10′ x 6′ x 6′( total height=7’10”)
1Soil Excavation360cuft5519800Brick Soling
2All the necessary plumbing items and pressure maching should be procured by the client.[as Required]60Sqft.1509000Single layer Brick Solling 10×6 ( 1sqft=8 pcs)
3PCC works60Sqft.15090002” Thickness.
4Footing Concreting32Sqft.35011200
5Brickwall192Sqft.190364804” Brickwall
7Concrete works329Sqft.3501151505” Raft Foundation Slab & 4” Share Wall
9Waterproofing Work with Sheet & Chemical269Sqft.11029590
10Plaster Works269Sqft.9024210
12Plumber job4Job16006400
13Plumbing Item1LS
14Debris management2Tips20004000
15Tank cover(Plastic Type)1Pcs45004500
Total cost:340862
Amount in Word: Three Lakh Forty Thousand Eight Hundred Sixty Two
Bar Bending schedule
S.NDescriptionLength( ft)DiaTotal length(ft)Per length weight(kg)Total WeightRemarks
aFooting Beam321041280.1924.3
2Share wallSpacing of 4 inches
a.Vertical Wall510763800.1972.2
b.Horizantal Wall3810103800.1972.2
3Foundation Slab
a.Main Bar121014168.00.1931.9
b.Distrubution Bar710241680.1931.9
4Top Slab
a.Main Bar1210141680.1931.9
b.Distrubution Bar710241680.1931.9
5Lapping Rebar100.1944.5Total rebar*15%

Disadvantages of oversized water tank capacity

If you Calculate Water Tank Capacity as compared to the required capacity of the tank following disadvantages are phase:

  1. Higher initial cost.
  2. Increased risk of water contamination.
  3. Difficulty in maintaining water quality.
  4. Wastage of resources.
  5. Occupies more space unnecessarily.
  6. Potential for stagnant water issues.
  7. Greater energy consumption for pumping.
  8. More frequent cleaning requirements.
  9. Challenges in regulating water temperature.
  10. Excessive strain on infrastructure.

I hope you easily understand the Calculate Water Tank Capacity for your home. If yes please comment. You are calculating your real data with real field conditions and water required for your home.

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