Buying Guide
Water Pump for High-Rise Buildings and Apartments: A Guide
How to choose a water pump for apartments and high-rise buildings: sump to overhead tank setup, head and flow sizing, standby pumps and essential controls.
For most apartments and high-rise buildings in India, the right water pump is a transfer pump that lifts water from the underground sump to the overhead tank, sized for the building's total head and daily demand, with a second identical pump kept as standby. In practice this is usually a three phase centrifugal monoblock beside the sump or an openwell submersible placed inside it, protected by level controls and dry-run protection. This guide explains how to size and set up such a system.
How water supply works in a typical apartment building
Most buildings in Hyderabad and other Indian cities follow this pattern:
- Source – municipal supply, one or more borewells, and often tanker water in summer.
- Underground sump – all sources fill a sump at or below ground level.
- Transfer pump – lifts water from the sump to the overhead tank (OHT) on the terrace.
- Gravity distribution – water flows down from the OHT to each flat.
Where there is a borewell, a borewell submersible usually fills the sump. Very tall buildings sometimes add a pressure booster, because floors just below the OHT get little gravity pressure.
Pump types that suit buildings
| Pump type | Where it sits | Typical role in a building | Points to note |
|---|---|---|---|
| Centrifugal monoblock (3–10 HP, single or three phase, 2880 RPM) | Pump room beside the sump | Sump to OHT transfer, water circulation | Best with flooded suction; needs priming and a foot valve if it has to lift water |
| Three phase openwell submersible (3–30 HP, 340–440V) | Inside the sump | Sump to OHT transfer in mid to large buildings | No priming and quiet, but needs dry-run protection |
| Single phase openwell submersible (1–7.5 HP, 220V) | Inside the sump | Independent houses and small blocks | Useful where only single phase supply is available |
| Heavy duty self priming monoblock (0.5–1 HP, 1440 RPM) | Beside the sump | Individual and low-rise homes | High suction, but not meant for high heads |
| Borewell submersible (V3 to V6) | Inside the borewell | Filling the sump from a borewell | Chosen by bore diameter and water level |
You can see the full Arrot-z range in the products section.
Step 1: Work out the total head
Total head is the height the pump must lift water plus the losses in the pipes.
- Static head: measure from the lowest water level in the sump to the inlet of the overhead tank. As a rough guide, allow about 3 metres (10 feet) per floor.
- Friction losses: pipes, bends, valves and the non-return valve all add resistance. For a short, well-sized rising main, adding 15–25% of the static head is a common starting allowance. Long or undersized pipes need more.
Example: a G+12 building has 13 levels of roughly 3 m each, about 39 m. Add 3 m for sump depth and 2 m for the tank inlet above the terrace, and the static head is about 44 m. Adding around 15% for friction gives a total head of roughly 50 m.
For a step-by-step method, see our guide on how to calculate pump head, flow and HP.
Step 2: Estimate daily demand and flow rate
Indian building norms commonly use about 135 litres per person per day for residential planning.
- 48 flats × 4 residents × 135 litres ≈ 26,000 litres per day.
- To deliver this in about 4 hours of total running time, the pump needs roughly 6,500 litres per hour, or about 110 LPM.
With a little margin, a target of 110–120 LPM is reasonable here.
Step 3: Estimate the motor HP
A handy approximation is:
Water HP ≈ (flow in LPM × total head in metres) ÷ 4,500
For 115 LPM at 50 m, that is about 1.3 water HP. Pumps of this size typically convert only around 45–55% of the motor's output into water power, so the motor needs roughly 2.3–2.8 HP. A 3 HP class pump is a sensible starting point, to be confirmed against the actual pump curve.
Single phase or three phase?
Most apartment buildings have a three phase 415V connection, and for pumps of 3 HP and above a three phase motor is usually the better choice. It draws lower current per phase, starts more smoothly and copes better with continuous duty. Single phase pumps (220–230V) are practical for independent houses and small blocks. See our single phase vs three phase pump guide.
Always install a standby pump
A building with 40–50 families cannot afford a day without water. Install two identical pumps in parallel, each with its own valves, and alternate them every week or two so wear is spread evenly and the standby is known to work.
Controls and protection you should not skip
- Automatic water level controller – starts the pump when the overhead tank is low, stops it when full, and cuts off when the sump is nearly empty.
- Dry-run protection – essential in summer, when borewell yield drops and sumps run low.
- Starter with overload and single-phasing protection – for larger motors, your installer may recommend a star-delta or soft starter instead of direct-on-line starting.
- Voltage protection – an under/over-voltage relay protects the motor from the fluctuations common on many local lines.
- Non-return valve – stops the water column flowing back and reduces water hammer.
- Gate valves and a pressure gauge – for isolating each pump and spotting problems early.
Installation tips
- Keep the pump as close to the sump as possible. Flooded suction, where the sump water level is above the pump inlet, avoids priming trouble.
- If a monoblock must lift water, keep the suction lift well within about 6 metres and make the suction pipe airtight, with no high points where air can collect.
- Use a suction pipe at least as large as the pump inlet and a rising main sized for the flow. Undersized pipes waste power for the life of the building.
- For submersibles in the sump, keep the pump clear of sludge and fully submerged at the lowest operating level.
Common mistakes to avoid
- Oversizing "to be safe" – a pump that is too large runs away from its efficient zone, can cause water hammer and wastes electricity.
- Ignoring summer conditions – plan for the lowest sump level and reduced borewell yield, not the post-monsoon situation.
- Neglecting maintenance – simple routine checks prevent most breakdowns. See our submersible pump maintenance tips.
Need help with your building?
Every building has a different height, layout and water source. Call +91-7799794047 or +91-9790854516 with the number of floors and flats, sump and tank details and your power supply, and the Aqua Pump Engineer team can help you shortlist a suitable pump and standby arrangement.
Frequently asked questions
Which pump is best for an apartment building's overhead tank?
Most apartment buildings use a three phase centrifugal monoblock pump next to the sump or a three phase openwell submersible pump placed inside the sump. The right choice depends on total head, required flow, sump layout and power supply. Always install a second identical pump as standby.
How much HP pump is needed for a 10 floor building?
HP depends on both height and flow, so there is no single answer. As a rough illustration, the worked example in this guide, a G+12 building with around 48 flats, works out to about a 3 HP class pump for sump to tank transfer. The exact rating should be calculated from total head, daily demand and the pump curve.
Should an apartment pump be single phase or three phase?
Where three phase supply is available, which is common in apartment buildings, three phase pumps are usually preferred for 3 HP and above. They draw lower current per phase and start more smoothly. Single phase pumps suit independent houses and small blocks.
Why is water pressure low on the top floors of my building?
Top floors sit only a few metres below the overhead tank, so gravity pressure there is naturally low. Common fixes include raising the tank, using larger distribution pipes or adding a pressure booster for the upper floors.