How a water pump and pressure tank work together

Water runs from the storage tank to the pump, on to the pressure tank, then to the house. A pressure switch sits between them and starts or stops the pump.

Inside the pressure tank, compressed air pushes water out when a tap opens. Small draws, like a hand wash, come from that cushion, so the pump does not start for every cup. When pressure falls far enough the pump starts and refills the cushion.

Without power there is no pump, so you get only what the cushion holds. That is the trade-off of a ground tank against a roof tank. The storage tank still has to be big enough for the lock-offs you get.

Cut-in is the pressure at which the switch starts the pump, and cut-out is where it stops. A 30-50 switch starts at 30 PSI and stops at 50 PSI. The setting should be on the switch or its paperwork.

One maker's manual (Pentair, for its steel pressure tanks) says to "adjust pre-charge to 2 PSI below pump cut-in pressure setting". Its table:

That is one manual, not a Jamaican rule. We could not obtain the manuals for other pump makers, so check the label on your own tank too.

With the power off and no water in the tank, using a tyre gauge on the air valve. Pentair's line is "Always set pre-charge with NO WATER in tank."

• Switch the pump off at the breaker.
• Open a tap until the flow stops, so the tank has emptied.
• Put the gauge on the air valve, usually under a small cap.
• Compare with the table above. Add or bleed air to match.
• Close the tap, then put the breaker back on.

If water comes out of the air valve, the membrane inside has probably failed, and that is a job for a plumber. Leave the switch cover closed throughout: there is live wiring under it.

Usually because the air cushion is gone, or because water is leaving when it should not. Short bursts wear out a pump and its switch.

Test with every tap shut and nobody using water. If the pump still starts by itself, suspect a running toilet, a leak on the line, or a non-return valve letting water fall back. The meter test on our high bill stack helps separate these.

If it only cycles quickly while a tap is open, check the precharge first. A tank that feels full and heavy, and has no air left, usually needs a plumber. Any new leak on your line costs money as well as pump life.

Switch it off at the breaker as soon as you realise the tank is low. A pump that keeps running with no water can damage itself, and it usually gives itself away with a change in sound and no pressure at the taps.

Wait until the storage tank has water again. Some pumps need priming afterwards, so if it runs and moves nothing, call the plumber rather than leaving it on. We could not obtain a pump maker's manual, so we give no safe running time.

If this keeps happening, ask for a low-water cut-off, wired by an electrician. Our lock-off stack covers the rest of a dry day.

Because the pressure never reaches the cut-out point, or the switch is failing. Likely causes are a leak or open tap, air getting in on the suction side, a worn pump, or stuck switch contacts.

Turn the breaker off if it has been running a long time, then look for the obvious: a hose left on, a toilet running, water pooling in the yard.

Beyond that, it is a plumber's job for the pump and an electrician's for the switch. Do not tape, jam or wire a switch to force it, and never cap a relief valve or bypass any safety device. Those are what stop a tank or pipe failing under pressure.

A licensed or certified electrician, for all of it. Breaker off before you touch anything on or near the pump, and we give no steps for wiring here. The Fire Brigade's Commissioner told JIS in October 2026 that owners of houses 30 to 40 years old should "find a certified electrician".

After a flood, power stays off. The test in JIS's flood tips for switching back on is that "an electrical personnel has confirmed that it is OK", and a pump standing in or near water is no exception. For your storm routine, see before the hurricane.

We would not, and part of the official answer is on record. The 2023 Rainwater Harvesting Planning Guideline says pumps "should not be connected to the public water main", and it requires a reflux (non-return) valve. That document is about rain systems, and we found no separate National Water Commission (NWC) rule for every house.

Still, the sensible layout is the same for everyone: NWC fills a storage tank, and the pump draws from that tank, never from the main. If you are thinking of a pump because the supply is weak, read low water pressure first. Ask NWC if you have any doubt about your connection. The rain side is on our rainwater stack.