Campervan Water Systems Explained: A Practical UK Guide

How a Campervan Water System Works

Every campervan water system, from the simplest weekender to a fully self-sufficient live-in build, follows the same loop: a fresh water tank stores your supply, a water pump moves it to the taps, and a grey water tank or portable container collects the water from the sink and shower. A motorhome water system follows the same loop scaled up — a motorhome's water system simply adds capacity, a shower and fixed waste plumbing.

The core components of the water supply system are:

That is genuinely all there is to it. What separates a good water installation from a bad one is sizing, frost protection and hygiene — which is what the rest of this guide covers. (Black water — the toilet side, whether a cassette or a fixed black water tank — is a separate system and a separate guide.)

Tank Sizing: How Much Water Do You Actually Need?

The most common mistake is fitting a bigger fresh tank than the van can usefully carry. Water is heavy — one litre of water weighs one kilogram — so 100 litres is 100kg of payload before you add the tank and fittings.

How you use water day to day drives everything, but realistic water usage for two people is:

For a weekend van, 25–45 litres is plenty — some minimalists skip fixed plumbing entirely and use a portable water container under the sink. Touring couples are well served by 45–70 litres. Only full-timers and shower-equipped vans genuinely need 100 litres of water capacity or more. Size the grey water tank at roughly the same as the fresh tank or slightly smaller — you can empty the water out more often than you refill.

12V Pumps vs Manual Pumps

Manual pumps — where you pump water to the tap by hand or foot — are cheap, silent, use no power and almost never fail. For a minimalist build with a small tank and one cold tap, they are a sensible choice, and a foot pump naturally rations how much you use.

12V water pumps are what most conversions fit. A pressure-switched diaphragm pump runs automatically when you open a tap, giving proper water flow to a mixer or shower. It draws little power but adds parts: a strainer before the inlet, fused wiring, and ideally an accumulator to smooth pulsing. The cheaper alternative is a submersible pump inside the tank, switched by a microswitch tap — common in smaller campers, but less durable than a quality external diaphragm pump.

If you want hot water or a shower, a 12V pressure pump is effectively mandatory.

Underslung vs Internal Tanks

An underslung water tank mounts beneath the floor, outside the van. The gains are real: no storage lost inside, bigger water capacity, and filling through an external water inlet. The costs are equally real: anything mounted outside of your van sits in freezing air all winter, needs proper mounting to the chassis, and is harder to inspect and clean.

A water tank inside the van — usually under a seat or bed — stays warm whenever the van is heated, is easy to inspect, and is the default in smaller campervans. The price is lost storage space.

The honest rule of thumb: internal tanks suit smaller vans and year-round UK camping; underslung tanks suit larger conversions where interior space is precious — ideally insulated, with tank heating if you winter camp. Many builds run an internal fresh tank and an underslung grey water tank, which is a sensible compromise.

Hot Water Options

Cold-only is fine for many builds — kettles exist. If you want a hot water system, the main routes are:

One point we will not soften: fixed gas appliances are not a DIY job. Any gas hot water heater in a campervan should be installed and certificated by a Gas Safe registered engineer holding the relevant LPG qualification — for your safety, your insurance and your resale value. Diesel units also demand correct fuel and exhaust routing. Hot water is where professional fitting earns its money; see our Gas Safe certification guide.

Winter: Protect the System from Freezing

Frozen pipes split, and frozen pumps and fittings crack — usually discovered in spring. If you use the van in winter, or store it through one:

Filling, Emptying and Etiquette

Fill the fresh tank from a drinking water tap using a food-grade hose — the blue, clearly food-safe type, never a garden hose that has lived in a shed. Campsites provide drinking water points, and many have motorhome service points with a dedicated grey water disposal drain.

The etiquette is simple but matters: never run grey water directly into a roadside drain or hedgerow — washing-up water carries food waste and detergent. Keep your filling hose and rinsing routine completely separate from anything that touches the toilet, and leave service points as clean as you found them.

Drinking Water Safety and Tank Hygiene

If you store water in a warm plastic tank for weeks it goes stale and can grow bacteria and biofilm. Sensible practice:

Many owners treat the tank as washing water and carry drinking water separately. That is a perfectly reasonable water setup — just decide which yours is and maintain it accordingly.

What It Costs

Broad brackets for parts at typical UK prices:

A campervan plumbing kit — a bundled water system kit with tank, pump, pipe and fittings matched to a typical campervan conversion — can simplify a DIY cold-water build. A professional water installation adds labour on top, but for gas work it is not optional, as above.

DIY or Professional?

Cold water plumbing is among the most DIY-friendly jobs when converting a campervan: low pressure, push-fit joints, and mistakes announce themselves as drips rather than dangers. If you can plumb a kitchen sink, you can plumb a van. Sketch a water system diagram before buying parts, connect the pump through a fused 12V feed, secure the tank properly — a full tank is heavy — and leak-test everything before boarding it in.

Hot water changes the equation. Gas appliances require Gas Safe installation, diesel heaters reward experience, and integrating water heating with the electric system is where professional converters earn their fee. A common-sense split: DIY the cold plumbing if you enjoy it, and bring in a professional for the heat. If you would rather have the whole system designed, installed and warrantied, our directory lists verified UK converters who do this every week.

Frequently Asked Questions

How does a campervan water system work?

A fresh water tank stores the supply, a 12V or manual pump pushes water to the taps when you open them, and waste from the sink drains into a grey water tank or portable container for disposal at a service point. Hot water, if fitted, comes from a calorifier or a gas or diesel water heater.

How long can you leave water in a campervan tank?

Treat tank water as washing water after a few days, especially in warm weather. Drain the system between trips rather than leaving it standing for weeks, refill at the start of each trip, and sterilise the tank and pipework a few times a year with a proper tank cleaner.

What size water tank do I need in a campervan?

Two people typically use 10–15 litres a day without showers, or 25–40 litres with them. A 25–45 litre tank suits weekenders, 45–70 litres suits touring couples, and 100 litres or more only earns its weight for full-timers and shower-equipped vans. Every litre is a kilogram of payload.

Can I install a campervan water system myself?

The cold water side, yes — tank, pump, pipework and grey water are well within DIY reach using food-safe components and careful leak testing. Fixed gas water heaters are the exception: they must be installed and certificated by a Gas Safe registered engineer with the LPG qualification.

Should my water tank go inside or under the van?

Internal tanks stay frost-free in a heated van, are easy to inspect, and suit smaller campervans and winter use. Underslung tanks free up storage and allow bigger capacity but sit in freezing air, so they need insulation — and ideally heating — for year-round UK camping.