Overhead tank vs underground sump — which is better?

Overhead tanks provide gravity-fed water flow without a pump, which is energy efficient. Underground sumps store larger volumes and are refilled by municipal supply, then pumped to the overhead tank. For a multi-floor home, both together is ideal — sump for large storage, overhead for daily use.

Water Tank Size Calculator — Home Storage Tank Capacity

Number of People

Water Supply Frequency

Number of Floors

Usage Type

Tank Type

ℹ️ How it's calculated

Daily need = People × litres per person per day (BIS IS 1172)
Storage need = Daily need × supply gap days
Safety buffer = +25% (for supply delays and emergencies)
Floor factor applied for multi-storey overhead tanks (pressure + volume loss)

📦 Common Tank Sizes Available

500 L1–2 person flat

750 L2–3 person flat

1,000 L3–4 person home (daily supply)

1,500 L4–5 person home (2-day supply)

2,000 L5–7 person or 2-floor

3,000–5,000 LLarge home / infrequent supply

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❓ Frequently Asked Questions

How much water does one person use per day?

As per BIS IS 1172, per capita water requirement is 135 litres/day for residential areas with full facilities. A practical estimate for tank sizing is 150–200 litres per person per day.

What size water tank for a family of 4?

A family of 4 needs about 600 litres/day (4 × 150 L). With daily supply, a 1,000 L tank is sufficient. If supply comes every 2 days, you need at least 1,500 litres.

Overhead tank vs underground sump?

Overhead tanks provide gravity-fed flow without a pump (energy efficient). Underground sumps store larger volumes. For multi-floor homes, both together is ideal — sump for large storage, overhead for daily gravity flow.

What material is best for water tanks in India?

Polyethylene (plastic) tanks are most popular — lightweight, rust-free, and affordable. Triple-layer tanks prevent algae and UV damage. For underground sumps, RCC cement tanks are most durable.