Caravan and Motorhome Water Systems Explained: Pumps, Taps and Truma Ultraflow

Water Systems Explained

A practical guide from Bedam Leisure — caravan & motorhome specialists

More phone calls reach us about water than almost anything else. The tap splutters. The pump runs and runs but nothing comes out. Or it won't run at all. Nine times out of ten it isn't a broken pump — it's one small part of a chain that people have never had explained to them. So here it is, start to finish: how a caravan or motorhome water system actually works, and what to check when it stops.

Once you can picture the path the water takes, fault-finding stops being guesswork. And crucially, you stop ordering the wrong part.

The path water takes

Every touring water system is the same handful of stages in a row. Water leaves an external container or an onboard tank, a pump pushes it, a one-way valve stops it running back, a filter cleans it, and then it splits between your cold taps and your water heater. If you know which stage has failed, you know what to buy.

1 The pump

Submersible or onboard? They fail differently

Most UK touring caravans use a submersible pump — a small 12V impeller pump on a lead that drops into your water barrel outside. Motorhomes and campervans, which carry water in a fixed tank, usually use an onboard diaphragm pump mounted inside on the pipework.

The distinction matters because they fail in different ways. A submersible pump is cheap and simple, and when it goes it usually goes completely — no hum, no flow. An onboard pump has a pressure switch built in, so its classic failure is cycling on and off in short bursts while a tap is closed, which points to a small leak or a tired switch rather than a dead pump.

On flow rate: don't just buy the biggest number. A standard submersible pump moves around 10 litres a minute, which is plenty for a single tap and a small shower. Step up to a 16 litre-a-minute unit only if you have a long pipe run, several outlets, or a shower that feels weak — the higher flow costs you a bit more current draw from the leisure battery.

Before you condemn a pump: check the fuse, then check the voltage at the socket with the tap open. A submersible pump that sounds weak is very often being starved by a flat leisure battery, not worn out.

2 The switching

Microswitch taps versus pressure switches

This is the single most misunderstood part of a caravan water system, and it decides which inlet socket you need to order.

In a microswitched system, each tap has a tiny switch inside it. Open the tap and it closes a circuit, powering the pump; close the tap and the pump stops. Simple, and it means the pipework is never held under pressure. The giveaway is that the pump only ever runs while a tap is physically open, and each tap tends to have a distinct click as you turn it.

In a pressure-switched system, the pump keeps the pipework pressurised. Open a tap, the pressure drops, the switch fires the pump; close the tap, pressure builds back up and the pump cuts out a second or two later. That trailing second of pump noise after you close the tap is the tell-tale sign.

Get this wrong and the new socket simply won't behave. If you fit a pressure-switch socket to a van with microswitched taps you'll get a pump that hunts and clicks; the other way round and it may not start at all. Look at what came off, or listen for that run-on after the tap closes.

3 The Truma Ultraflow

What the Ultraflow actually is

Weeping at the housing? Nine times out of ten it is perished O-rings on the pistol connector, not a failed pump. The Ultraflow O-ring kit (£13.99) is a five-minute fix; if the connector itself is cracked, the replacement pistol connector (£75.99) is the next step.

If you already have an onboard pump and just want to draw from an external barrel, you want the Ultraflow inlet hose (£26.99) — it has a strainer on the submerged end instead of a pump. And if you'd rather stop trudging across the site with a barrel altogether, the Ultraflow Waterline 15 m hosepipe (£112.99) connects the site tap straight to your housing.

4 Filtration & flow protection

Filters, strainers and non-return valves

Three small parts do a disproportionate amount of work here, and all three are cheap.

A carbon filter removes the taste and smell of chlorine and whatever the site's pipework has added. Change it at the start of each season and again if the van has stood for months — a cartridge left damp over winter is exactly where stale water and biofilm take hold.

A strainer sits before an onboard pump and catches grit. It costs a few pounds and it is the reason your diaphragm pump doesn't chew itself up. Most people have never opened theirs; if you own an onboard pump, go and look.

A non-return valve lets water travel one way only. If your system drains back down to the barrel every time you stop the pump, so that you get a long airy splutter before flow returns, a failed non-return valve is the usual culprit.

Mixing brands? A Whale mains system and a Truma Ultraflow inlet will happily work together with the correct Watermaster-to-Ultraflow adaptor (£14.99). Please don't force mismatched fittings — that is how hairline cracks and slow leaks start. The 12 mm John Guest non-return valve (£15.99) is the standard push-fit replacement for most fresh-water pipework.

5 Looking after it

Sanitising, draining and winter

Water systems don't wear out so much as they get neglected. Two habits cover almost everything.

First, sanitise twice a year — once when you recommission in spring and once before you lay up. Run a proper water-system cleaner through every outlet, hot and cold, leave it to dwell, then flush thoroughly and fit a fresh filter cartridge afterwards. Putting a new cartridge in before you flush just contaminates the new filter.

Second, drain properly before a frost. This is the expensive one to get wrong: water expands as it freezes and will split a pump body, a filter housing or a plastic elbow without any warning. Opening the drain-down taps and leaving them open is the minimum, but be aware that the traditional method typically leaves around a litre sitting in low points of the pipework. A purpose-made drain-down kit blows the residue out with air, which is why they've become popular with people who store outdoors.