Choosing the Correct Water Pump

Water pump listings tend to lead with two numbers: litres per minute and PSI. They are important, but buying the biggest number in each column does not necessarily give you a better water system. In a campervan or motorhome, too much flow empties the fresh water tank surprisingly quickly, while more pressure than the plumbing needs can create problems of its own.

The right pump comes down to how many outlets it needs to supply, how likely they are to be used together, and what equipment sits downstream of it. Get those things right and choosing between the common 7 and 10 litre pumps becomes much simpler.

Start with how much water you actually need to move

Flow rate tells you how many litres of water the pump can deliver in a minute. It is tempting to assume that more is better, particularly when trying to create a decent shower, but a leisure vehicle carries a limited amount of water.

For a typical campervan with a kitchen sink, perhaps a wash basin and a shower, a 7 litre per minute pump is usually plenty. Most of the time only one outlet is being used anyway. The extra output of a larger pump brings little benefit when someone is simply washing their hands or filling the kettle, but it can get through the contents of the fresh water tank considerably faster.

A 10 litre per minute pump starts to make more sense in a larger motorhome, or where two outlets may genuinely be used at once. Open a kitchen tap while somebody is showering and the extra available flow helps prevent the shower from dropping away.

The useful question, then, is not how powerful a pump can I fit? It is how much water am I realistically going to use at the same time?

For most campervans, 7 litres per minute is the sensible answer.

Pressure is about the system, not how powerful the shower feels

The second number on the pump is its pressure, normally quoted in PSI. Again, the highest figure is not automatically the best choice.

A 20 PSI pump is well suited to a straightforward campervan installation with relatively short pipe runs and a small number of outlets. Moving up to 30 PSI gives more pressure to work with and can be useful in a larger motorhome with longer plumbing runs, more fittings and a more extensive water system.

There is another reason not to simply keep increasing the pressure: everything after the pump has to cope with it.

That includes pipework and fittings, but also equipment such as water heaters. If the vehicle uses a Truma Combi, we would normally stay at 30 PSI or below. Going beyond the pressure the system was designed around can interfere with components such as the boiler's safety pressure relief arrangement.

A well-matched 20 or 30 PSI pump should provide consistent water without unnecessarily pressurising the rest of the installation.

A disappointing shower isn't always the pump's fault

This is worth knowing before replacing a pump simply because the shower feels weak.

The pump is only one part of the system. Long pipe runs, restrictive fittings, partially blocked filters, narrow bore pipe and the shower head itself can all reduce the flow that eventually reaches the outlet.

A larger pump cannot always overcome those restrictions.

If the kitchen tap has good pressure but the shower does not, for example, the pump is unlikely to be the first place to look. Following the pipework between the two often tells you more than fitting a more powerful pump.

Why does the pump keep switching on and off?

A diaphragm water pump does not run continuously whenever the water system is live. It builds pressure and switches itself off, then starts again when opening a tap causes that pressure to fall.

With a tap only slightly open, that can result in the familiar on-off-on-off cycling heard in many campervans.

The pump may be doing exactly what it was designed to do, but it does not make for a particularly refined water system.

This is where an accumulator earns its place.

An accumulator changes how the system feels

An accumulator stores a small amount of pressurised water between the pump and the outlets. Instead of every small demand immediately triggering the pump, the system can draw from that stored pressure first.

The difference is noticeable rather than dramatic. Water delivery becomes smoother, pressure fluctuations are reduced and the pump starts less frequently. That usually means less noise as well as less repeated switching of the pump.

It is particularly worthwhile where people use small amounts of water regularly — rinsing a cup, washing hands or briefly opening a tap — because those are exactly the situations that otherwise cause repeated short pump cycles.

An accumulator will not turn an undersized pump into a larger one, and it will not cure restrictive plumbing. What it does is make a correctly sized pump behave better.

For most vans, the choice is simpler than it looks

A conventional campervan with a sink and shower rarely needs an enormous pump. A 7 litre per minute pump at 20 PSI is a sensible starting point for a smaller, straightforward installation. Where the vehicle is larger, the pipe runs are longer or a little more pressure is required, 7 litres per minute at 30 PSI is often the next step.

Move to 10 litres per minute at around 30 PSI when there is a genuine need for additional flow — particularly in a larger motorhome or where more than one outlet may be used at the same time.

And if quiet, smooth operation matters, leave room in the installation for an accumulator.

The best water pump is not necessarily the one capable of moving the most water or producing the highest pressure. It is the one that supplies the outlets comfortably without emptying the tank unnecessarily or asking the rest of the plumbing system to deal with pressure it does not need.

If you're still unsure, tell us the size of your vehicle, which outlets you have and which water heater is fitted, and we can point you towards the pump that suits the system rather than simply the biggest one on the shelf.