The tank is full. You can hear water moving in the pipes. And the shower still delivers a thin, lukewarm dribble, the washing machine takes forty minutes to fill, and the instant shower cuts out completely the moment somebody opens a tap in the kitchen.
This is one of the most common complaints we hear about a system that is, technically, working perfectly. The water is there. The pressure is not. Because the two feel identical at the tap, people spend money on the wrong fix: a bigger tank, wider pipes, a plumber who reroutes the house.
Pressure in a gravity system is not a matter of opinion or plumbing skill. It is a number set by one thing, and once you work it out you can decide in five minutes whether you need a booster pump or a taller stand.
Where Household Pressure Actually Comes From
In a tank-fed system, pressure at any outlet comes from exactly one source: the vertical distance between the water surface in the tank and the outlet itself. Nothing else contributes.
The conversion worth memorising: ten metres of vertical water column produces roughly one bar, about 100 kilopascals or a little over 14 psi. Every metre of height therefore gives about 0.1 bar.
Now apply that to a typical Kenyan home. A tank on a two metre stand, feeding a shower head nearly two metres above the bathroom floor, leaves a vertical drop measured in centimetres. The pressure there is a small fraction of a bar. That is not broken plumbing, it is arithmetic.
Two things surprise people. Tank volume is irrelevant: a 10,000 litre tank two metres up gives exactly the same pressure as a 200 litre tank two metres up, because volume buys duration, not force. Horizontal distance adds nothing either, so a tank across the compound at the same height performs like one outside the wall.
What distance does do is take pressure away once water moves. The moment water flows, friction in pipes, elbows, tees and valves eats into the static figure, and narrow or long runs eat a lot. That is why pressure seems fine filling a bucket and vanishes when two outlets open together.
What Your Appliances Are Actually Asking For
A tap and a bucket will tolerate almost any pressure. Modern appliances will not, and this is where low pressure stops being an annoyance and starts costing money.
An instant electric shower contains a flow switch that only energises the element once water moves fast enough through it. Below that threshold the element never switches on, so you get cold water and conclude the shower has failed. It has not. It is protecting itself from burning out dry.
Washing machines fill through solenoid inlet valves that need a minimum working pressure to open reliably; below it the machine crawls or aborts with a water supply fault. Solar water heaters, mixer showers, sprinklers and pressure washers each carry their own figure.
That figure is the number to work from. It is on the appliance plate or in the manual, almost always in bar. Write down the minimum for every appliance, take the highest, and compare it with the static pressure your tank height gives. That one comparison sizes the problem.
Raising the Tank: The Cheapest Bar You Will Ever Buy
Every metre of height you add gives roughly 0.1 bar, permanently, with no motor, no wiring, no electricity bill and nothing to service. Most households never consider it because a pump feels like the modern answer.
It works best in one specific situation: a single storey house where the tank sits on the ground or a low stand and there is room to build higher. Moving from a two metre stand to a five metre stand triples the pressure at the shower, and for many homes that is the whole problem solved.
It stops being the answer once the numbers get large. Gaining a full bar means ten metres, a tower rather than a stand, and cost and wind loading climb steeply with height. If you are in an apartment, or the tank already sits on the roof above the bathroom, there is no height left to find.
The structural side is not optional. Water weighs a kilogramme per litre, so a full 1,000 litre tank puts a tonne on that frame, plus the tank and the movement of water inside it. Plastic tanks need continuous flat support across the whole base, not four corner beams, because unsupported bases split. A heavy tank on a stand welded up by eye is a genuine hazard.
One knock-on effect to plan for: raising the tank increases the head the filling pump must overcome, so the borehole or sump pump feeding it now works harder. If that pump is near its limit, read our guide to sizing a pump on head and flow before you build the stand.
What a Booster Pump Is, and What the Pressure Tank Does
A booster pump sits on the outlet side of your storage tank. It does not lift water from a source; it raises the pressure of water already available on its way to the taps. In a house it is usually a small centrifugal or multistage pump, designed to start and stop automatically as outlets open and close.
Alongside it sits a pressure tank, the component people leave out to save money. It is a steel vessel divided by a rubber diaphragm: water on one side, a cushion of compressed air on the other.
Its job follows from one fact of physics: water is very nearly incompressible. In a sealed pipe with no air cushion, taking out a cupful collapses the pressure almost instantly, and putting a cupful back sends it straight to the top. So the pump starts, runs for a second, hits cut-out, stops, and starts again the moment another cupful leaves.
The air cushion changes that. As the pump runs, water compresses the air behind the diaphragm, storing a real volume of pressurised water. When a tap opens, that stored water flows out first and pressure falls gradually. The usable volume between cut-out and cut-in is drawdown, and drawdown is what buys the pump a proper run instead of a twitch.
This matters because wear is counted in starts, not hours. Starting current is several times running current and heats the windings hard, contacts arc and pit each time they close, and bearings and seal take a shock load with every start. A booster short cycling hundreds of times an hour can wear out in months.
The Pressure Switch: Cut-In, Cut-Out and the Gap Between
The pressure switch is the small box wired into the pump's supply, and it is what makes a booster automatic. Inside, a diaphragm works against a spring, opening and closing the contacts at two set pressures.
Cut-in is the falling pressure at which the contacts close and the pump starts. Cut-out is the rising pressure at which they open and it stops. Open a tap, pressure drops to cut-in, the pump runs; close the tap, pressure climbs to cut-out, the pump stops. That is the whole cycle.
The gap between the two, the differential, deserves as much thought as the numbers. Too narrow and the pump starts far more often for the same water use. Too wide and the shower sags and surges as the system swings between the points. Most switches adjust both: typically a large central nut moves both settings together and a smaller nut changes only the differential. Check your own switch label.
Two limits are worth respecting. Never set cut-out above the pump's rated maximum, and never above what the weakest part of the installation can take, usually a fitting, a flexible connector or a water heater rather than the pipe. And whenever you change the settings, drain the system and reset the tank pre-charge to match. The two are a matched pair.
There is a modern alternative: the electronic automatic pump controller, often sold as a press control. It combines a pressure sensor, a flow sensor, a non-return valve and a dry-run cut-out in one unit mounted on the pump outlet. Because it stops the pump when flow ceases rather than at a set pressure, it needs no pressure tank to prevent cycling. The trade-off is that a dripping tap keeps waking it, and you lose the cushion that softens water hammer.
Dry Running: The Failure That Kills Boosters
The single most common way a household booster dies is not overwork. It is running with no water in it.
Between the wet end and the motor sits a mechanical seal, two very flat faces pressed together, lubricated and cooled by the water passing it. Run the pump dry and those faces grind with nothing between them, overheat and destroy themselves, sometimes in under a minute. Once the seal goes, water tracks along the shaft into the motor and you are buying a new pump.
It happens for ordinary reasons. The tank empties overnight because the mains did not come. A valve is left closed. A strainer blocks. In every case the switch keeps calling for a pump with nothing to move, and it runs until somebody notices.
Protection is cheap and there are three routes. A low-level float switch in the supply tank, wired into the pump control circuit, is the simplest and most reliable: it cuts power when water drops below a set level. An electronic controller with a dry-run cut-out trips on no-flow. A dedicated relay does the same for an existing pressure switch.
Fit one at installation, not after the first seal has failed. It costs a small fraction of a replacement pump, and it is the difference between an empty tank being an inconvenience and an empty tank being a purchase. Mount the booster below the tank so it stays flooded, and priming problems never start.
Booster or a Higher Stand? How to Decide
Work through it in this order. Calculate your current static pressure from the height difference. Find the highest minimum inlet pressure among your appliances. Subtract. The shortfall is what you are buying.
If that shortfall is modest, say 0.2 to 0.5 bar, and the site allows a taller stand built properly, raise the tank. It is usually cheaper once you count wiring and running costs, and it keeps working during a power cut, which in Kenya often settles it.
Fit a booster when the shortfall is a bar or more, when the tank is already as high as it will go, when you have upper floors or several bathrooms in use at once, or when an appliance states a minimum height cannot reach. A gravity system also loses pressure as the tank empties, while a booster on a pressure switch holds the same pressure full or nearly empty.
Very often the answer is both. Raise the tank as far as the structure sensibly allows, then boost the remainder. A booster fed from a well-elevated tank works less hard for the same result and lasts considerably longer.
Whichever route you take, buy the booster as a complete set rather than a bare pump. A pump wired to a switch with no pressure tank and no low-water cut-out is the cheapest thing on the shelf and the most expensive to own. We stock booster pumps, pressure tanks, switches, float switches and fittings across all six branches, with prices on the price list and the range on the water equipment page. Send us your tank height, your bathrooms and the appliance you need to satisfy, on WhatsApp or through the contact page, and we will size the set with you.
Key Takeaways
- Pressure in a tank system comes only from vertical height: roughly one bar per ten metres, or about 0.1 bar per metre. Tank size and horizontal distance add nothing.
- Get the minimum inlet pressure off each appliance plate, take the highest, and compare it with your height. The shortfall is the problem you are actually solving.
- Raising the tank buys pressure that costs nothing to run and works during a power cut, but the stand must be engineered: a full 1,000 litre tank is a tonne.
- A booster on a pressure switch without a pressure tank short cycles and destroys itself. Wear is counted in starts, not hours.
- A booster clicking every few seconds usually means the pressure tank has lost its air pre-charge, not that the pump has failed.
- Always fit dry run protection. The mechanical seal is cooled by the water passing it and can fail within a minute of running dry.
Frequently Asked Questions
How much water pressure does tank height give me?
Roughly one bar for every ten metres of vertical drop, which works out at about 0.1 bar per metre. Only the vertical distance between the water surface in the tank and the outlet counts. A tank sitting two metres above a shower head gives about 0.2 bar, and that is the same whether the tank holds 200 litres or 10,000 litres. Tank size changes how long the water lasts, not how hard it pushes.
Why does my booster pump switch on and off every few seconds?
Almost always because the pressure tank has lost its air cushion, either through a slow leak at the valve or a ruptured diaphragm. Water is close to incompressible, so with no air to absorb a small volume the pressure jumps from cut-in to cut-out in an instant and the switch chatters. Drain the system, check the pre-charge at the valve with a tyre gauge and reset it to the figure in the manual, usually a little below cut-in. If it will not hold air, the tank needs replacing.
Do I need a pressure tank with a booster pump?
If the pump is controlled by a mechanical pressure switch, yes, and running without one will destroy the pump. The tank provides the drawdown volume that lets the pump run for a useful period instead of restarting every few seconds. The exception is an electronic automatic pump controller, which stops the pump on no-flow rather than on pressure and so does not need a tank to prevent cycling, although a small tank still helps with drips and water hammer.
Is it better to raise the water tank or install a booster pump?
Raise the tank if the gain you need is modest, perhaps 0.2 to 0.5 bar, and the site and structure allow it, because height costs nothing to run and never fails during a power cut. Fit a booster when you need a bar or more, when the tank is already at roof level, when you have upper floors or several bathrooms, or when you want pressure that stays steady as the tank empties. Doing both is often the best answer.
What is dry run protection and does my pump need it?
It is any device that cuts power when there is no water to pump: a low-level float switch in the supply tank, an electronic controller with a dry-run cut-out, or a dedicated relay. Every automatic booster needs one. The mechanical seal between the wet end and the motor is lubricated and cooled by the water passing it, so with no water it overheats and fails, sometimes within a minute, and then leaks into the motor.