An overhead water tank is a storage container placed at a height—usually on a rooftop—to store water for domestic or commercial use. Water is pumped into it and then distributed using gravity. These tanks are commonly used in homes, apartments, offices, schools, and hospitals.

But just installing a tank isn’t enough. You need to calculate the right overhead tank capacity—too little, and you’ll run out of water quickly; too much, and you’ll waste money and space.

In this blog, we will guide you step-by-step on how to calculate overhead water tank capacity for your home, building, or business.

Why Calculating Overhead Tank Capacity is Important

Ensures sufficient daily water supply
Prevents frequent refilling
Saves money on pumping and space usage
Matches usage to demand
Avoids stress on building structure

So whether you’re planning for an overhead tank of capacity 1000 litres or a large tank for a 4-storey building, correct calculation is key.

How to Calculate Overhead Water Tank Capacity

The calculation is based on three simple factors:

Number of people using the water
Daily water requirement per person
Number of days of storage you want

Formula:

Overhead Tank Capacity (in liters) = Number of People × Daily Water Use × Backup Days

In India, the Central Public Health and Environmental Engineering Organization (CPHEEO) recommends:

135 liters per person per day

Let’s apply this.

Example: Overhead Water Tank Capacity for a Family

Suppose a family has 4 members. They want a water backup of 2 days.

Tank Capacity = 4 × 135 × 2 = 1080 liters

So, an overhead tank of capacity 1000 litres (or slightly more) would be a perfect fit.

Example: Capacity of Overhead Tank of 4 Storey Building

Let’s assume each floor has 2 flats, and each flat has 4 people.

Total people = 4 floors × 2 flats × 4 = 32
Daily water use = 32 × 135 = 4320 liters
For 2 days: 4320 × 2 = 8640 liters

So, the capacity of overhead tank of 4 storey building should be at least 9000 liters.

Overhead Water Tank Size Based on Shape

For cylindrical tanks:

Use the formula:

Volume = π × r² × h

Where:

π = 3.1416
r = radius (in meters)
h = height (in meters)

Convert cubic meters to liters:

1 m³ = 1000 liters

For rectangular tanks:

Volume = Length × Width × Height

Again, convert to liters.

Common Sizes for Overhead Water Tanks in India

Tank Size (Liters)	Ideal For
500 Liters	Small family (2–3 people)
1000 Liters	Family of 4–5 people
2000 Liters	Large families (6–8)
5000 Liters	Small building (10–15 people)
10,000+ Liters	Multi-storey buildings

These values reflect the capacity of overhead water tanks in India typically used in both urban and semi-urban areas.

⚖️ Maximum Capacity of Overhead Water Tank

There is technically no upper limit, but your roof must be strong enough to support it. Since 1 liter = 1 kg, a 10,000-liter tank = 10,000 kg (10 tons). Always consult a structural engineer when going for high-capacity tanks.

Installation Tips

Use a flat concrete base
Tank should have UV protection
Install inlet, outlet, and overflow pipes
Use food-grade plastic or stainless steel
Secure the tank with proper clamps

Cleaning is Just as Important

Once you’ve chosen the right capacity of overhead tank, regular cleaning ensures safe and healthy water.

Here are some helpful resources:

Need local services?

Final Thoughts

Choosing the right overhead tank capacity is not complicated. Use simple math, think about your water needs, and allow for 1–2 days of backup. Also, consider future expansion—more family members, or more floors. From an overhead tank of capacity 1000 litres to larger setups, planning helps avoid shortages and costly mistakes.

Make sure your tank is clean, safe, and matches your home or building requirements.