Van Plumbing Systems

Plumbing in a van is simpler than in a house, but the constraints are tighter. You've got limited fresh water supply, limited space to route lines, temperature swings that can freeze tanks, and nowhere for gravity to help — everything moves by pump pressure. Get the plumbing system right and you'll forget about water. Get it wrong and you'll spend months troubleshooting leaks or waking up to frozen pipes.

We've built enough vans to know which systems work and which ones cost money fixing later. This guide covers what we actually install: tank sizes, pump choice, materials, hot water options, and the differences between van conversions and cargo trailers.

What Does a Van Fresh Water System Include?

Your fresh water system has three parts: a tank to hold water, a pump to move it, and lines to carry it to sinks and showers. The tank size, pump pressure, and line material determine how your water feels and how long the system lasts.

Tank Size and Placement

Fresh water tank sizes for vans range from 20 to 80 gallons. Most builds use 30, 40, or 60 gallons. The bigger the tank, the longer you can go without filling up — but tanks take up space and add weight.

A 30-gallon tank lets a couple shower once, wash dishes, and use the sink for maybe three days before needing water. A 60-gallon tank stretches that to five or six days. A 20-gallon tank is almost too small unless you're parked at a campground and refilling constantly.

Tank placement matters for weight distribution and access. We put water tanks low in the van frame to keep the center of gravity where it belongs. Food-grade polyethylene tanks resist corrosion and won't rust like metal tanks. Some builders use aluminum or stainless steel, but those cost more and add weight. Poly is the practical choice for vans.

Access for filling and cleaning is critical. You need a water inlet that's easy to reach with a hose, and ideally a way to access the tank interior if sediment or algae builds up. We mount tanks between frame rails or under cabinets, always with a fill inlet on the exterior and access in the interior.

Pumps: Pressure and Reliability

A 12V water pump pressurizes your system so water comes out sinks and showers when you turn them on. Pressure pumps are either diaphragm type (quiet, self-priming) or centrifugal (cheaper, noisier). We use quality diaphragm pumps because they're quieter and more reliable in a van where you hear everything.

Pump flow rate matters. Most vans use 5–8 GPM (gallons per minute) pumps. Anything smaller and showers feel weak. Anything larger and you'll drain a full tank in a few minutes of use. A good pump pulls around 7–10 amps at full draw, so you need at least a 30A dedicated breaker on your 12V electrical system.

Low-pressure switches shut the pump off when tanks run dry, protecting the pump from damage. A lot of builders skip these and regret it when a forgotten tank runs empty and burns out the pump. It's a $50 part that saves you $200 in pump replacement.

Accumulator tanks (small pressurized cylinders) smooth out pump cycling and reduce how often the pump runs. With an accumulator, the pump builds pressure, then shuts off. Turning on the sink draws water from the accumulator first, and only when pressure drops does the pump kick back on. Without an accumulator, the pump runs every time you use water, which wears it out faster and makes annoying cycling noise in the middle of the night.

Plumbing Lines and Materials

PEX tubing is the standard for van plumbing. It's flexible, doesn't freeze-crack as easily as rigid lines, costs less, and you can run it under cabinets and behind walls without needing fittings every few inches. PEX comes in white (all-purpose), blue (cold), and red (hot). Use the color coding to avoid confusion.

Size matters less than people think. Most vans use ½-inch lines from the pump to the fixture area, then ¼-inch lines to individual sinks and showers. Smaller lines save space and material but create slightly more pressure drop. The difference is barely noticeable.

Fittings at every connection point should be brass compression or push-fit fittings. Avoid plastic fittings because they fail under pressure over time. You want to see brass inside the van and crimp-secured connections (not just push-fit) at pressure points near the pump.

Insulation on hot water lines prevents heat loss as water travels from the heater to the fixture. Foam pipe wrap is cheap and effective. If you're in a cold climate, wrap all exposed lines, especially those running outside or through uninsulated walls.

Winterization and Freeze Protection

The biggest failure mode in van plumbing is frozen water. Below 32°F, water in exposed lines and tanks can freeze, crack components, and leave you without water in the middle of winter. Winterization is mandatory if you're building for cold climates.

Insulation is the first defense. Wrap tanks and all external lines. Add heating tape (electric or propane-heated) around critical areas like the pump inlet or the hot water heater. Some builders add a small heating element inside the tank itself to keep water from freezing during long cold snaps.

The second defense is drainage. If you know you're heading into freezing weather, drain the system completely. Close the tank valve, open all faucets, and let gravity empty the lines. Then use an air compressor to blow out remaining water. This is the most reliable way to prevent freeze damage.

Glycol (RV antifreeze) is a third option. Run antifreeze through the entire system before winter. It won't freeze, but it tastes terrible and requires flushing the system with clean water before you can use it again. Most boondockers drain instead of winterizing because it's simpler.

How Does a Van Grey Water System Work?

Gray water is the wastewater from sinks and showers. It needs to go somewhere, and that somewhere is a gray water tank. In vans, gray tanks are usually 20–40 gallons, depending on your tank size and how often you can dump.

Gray water drains by gravity, so the tank sits lower than the sinks and shower. All drain lines slope slightly downward (roughly ¼ inch drop per foot of run) so water doesn't pool in the lines and grow bacteria. A drain line that pools water will stink, so slope matters.

P-traps under sinks prevent sewer smell from coming back up the drain. Install these where you'd expect them in a house — under the sink, before the gray tank. Traps hold water that creates a seal against odor.

Tank size depends on your usage. A couple taking short showers every day might fill a 25-gallon gray tank in three or four days. A couple camping at established campgrounds might go a week between dumps. The bigger the tank, the longer you can stay put.

Gray tanks are usually opaque poly so you can't see the level. We install dipsticks or water level sensors so you know when to dump. Dumping is straightforward — you drive to a dump station, connect a hose, and let gravity do the work. Some campgrounds have dump stations on-site. Others require a 10-minute drive to the nearest facility.

Odor control is important. Keep the tank vented so air pressure doesn't build up, and use drain strainers to keep food debris out. Some builders add enzyme treatments to break down organic matter, which reduces smell over time.

What Are the Best Toilet Options for a Van?

Toilet choice is one of the biggest decisions in plumbing because it affects water usage, dump frequency, and whether you can use your van in winter or dry climates.

Composting Toilets

A composting toilet has no water and no tank to dump. You go, add sawdust or coconut coir, and over time the waste breaks down into a dry residue. When the chamber fills (roughly every month for regular use), you empty it into a trash bag. That's it.

Composting toilets save fresh water and eliminate the need to find dump stations. They work great if you're okay with a slightly different bathroom experience and you have access to sawdust or coir. In mild climates, they work perfectly. In very cold weather, decomposition slows down and odor can become an issue.

The downside: composting toilets take up space, require ventilation, and some people find them less convenient than flush toilets. They're cheaper to install than other options and cost almost nothing to operate after that.

Cassette Toilets

A cassette toilet is a small flush toilet with a detachable waste tank underneath. You flush, the waste goes into the cassette, and when it's full (usually a week or two for two people), you detach the cassette and dump it at a dump station.

Cassette toilets feel and work like regular toilets, which many people prefer. They hold about 15–20 gallons and use a small amount of fresh water per flush. You'll dump the cassette more frequently than a big black tank, but that's the tradeoff for a toilet that feels normal.

The downside: cassettes are bulkier than composting toilets, you need access to dump stations, and you're using some fresh water every time you flush. In a van where water is limited, that adds up. Most people do okay with this approach because dump stations are common and cassettes don't require much fresh water.

Full Flush Toilets with Black Tanks

A traditional RV toilet with a full black tank lets you use the bathroom normally without thinking about it. Flush, the waste goes into the tank, and once a month or so you dump at a facility. It's the most house-like option.

The downside: you need a decent-sized black tank (20–35 gallons), plumbing space to route vent and fill lines, and you'll need to find dump stations regularly. In a small van, the tank takes up real estate. In a large van or trailer, it's not an issue.

Black tanks need a dedicated vent line that goes through the roof so gases escape. Without proper venting, the tank can pressurize and create smell problems. Vent lines should be insulated and sloped slightly so water doesn't pool in them and freeze.

Should You Get a Tankless or Tank Water Heater for a Van?

Hot water is a nice-to-have, not a must-have. You can live without it and save cost and complexity. But if you want hot water, you have two main options.

Propane Tankless Heaters

A tankless water heater heats water on demand as it flows through a heat exchanger. Turn on the hot tap, propane ignites, and within a few seconds you have hot water. Turn off the tap, the heater shuts down.

Tankless heaters are compact, efficient, and give you unlimited hot water (as long as you have propane). They use your van's propane supply, which is the same supply that runs your stove and heater. The tradeoff is a slight delay before hot water arrives (you'll flush a little cold water first) and you need proper ventilation for exhaust.

Install a tankless heater in a location where venting is straightforward — usually the exterior wall near the kitchen. The heater needs both a propane line and a water line connected, plus a vent line through the wall or roof. Modern units are compact and reliable. Budget $400–800 for a quality unit plus installation.

Tank Water Heaters

A tank heater holds 2–6 gallons of water and keeps it hot using propane or electric elements. In a parked van, the heater maintains temperature. Turn on the tap and you already have hot water.

Tank heaters are great if you park for days at a time and want hot water readily available. If you move every day, the heater spends all its time reheating water you never use. Tank heaters are bigger than tankless units and take up space.

Most tank heaters are dual-fuel (propane + electric 120V). When you're plugged into shore power, the electric element heats water efficiently. When you're off-grid, propane takes over. Some models switch automatically. Others require manual selection.

What Sinks, Showers, and Fixtures Work Best in a Van?

Sink and shower selection is more about lifestyle than plumbing cost. A basic single-basin sink and a small shower head are enough. Upgraded options include dual sinks, rain shower heads, or integrated outdoor showers.

Sinks in vans are usually compact stainless steel or composite. Position the sink so the gray tank sits below it and drain slope is natural. Avoid placing a sink where the tank below it creates slope problems.

Shower systems vary. Some builds have an indoor shower enclosure with a drain pan. Others use an outdoor shower — a foot shower or handheld mounted on the exterior. Outdoor showers save interior space and are popular with minimalist builds.

Shower drain pans in vans should be tileable and sloped so water drains quickly. Stagnant water in the pan grows mold. Ventilation is critical — run a vent from the pan to the exterior or combine it with the van's main ventilation.

Faucets should be low-flow to conserve water. A faucet that delivers 1–2 GPM instead of 2.5 GPM stretches your fresh water supply. Combine this with shorter showers and you'll stay comfortable on less water.

How Much Does Van Plumbing Cost?

Plumbing costs scale with system complexity. A basic system (small tank, composting toilet, no hot water) is minimal. A full system with hot water, shower, and adequate tank size is where costs climb.

Basic builds minimize water and complexity. Standard builds add hot water and modest tank sizes. Premium builds include multiple water points, large tanks, and redundant systems.

How Does Van Plumbing Differ from Cargo Trailer Plumbing?

Cargo trailers and van conversions use the same plumbing principles, but the execution differs slightly.

Trailers have a flat floor and ceiling space to work with, so tank placement is flexible. You can mount tanks under the floor if you're not worried about freeze exposure. Vans have wheel wells and curved walls, so tanks go where they fit — usually under cabinets or integrated into the frame.

Trailers need independent water supply. You can't fill the tank through a hole in the floor every trip, so we install a large fill inlet on the side of the trailer. Vans use a side-mounted inlet too, but the constraints are tighter.

Vent lines in trailers can route through the roof easily. In vans, roof space is at a premium, so vent lines often run along the exterior wall or share roof penetrations with other systems.

Both platforms use the same pump type, the same PEX tubing, and the same fixtures. The difference is routing and space efficiency. Trailers are more forgiving. Vans require tighter planning.

What Are the Most Common Van Plumbing Mistakes?

We've seen almost every plumbing failure. Here are the most common mistakes and how to fix them.

Drain lines without slope: If gray water lines don't slope downward, water pools and stinks. Every drain line should slope at least ¼ inch per foot toward the tank. Check this during layout, not after the walls are closed.

Undersized tanks: A 20-gallon fresh tank sounds fine until you're out of water after one shower. More tank gives you more freedom. Bigger is almost always better, up to the point where weight and space become problems.

No accumulator tank: Pumps cycle on and off constantly without an accumulator, creating noise and wearing out faster. A $30 accumulator saves headaches.

Leaks in fittings: Plastic fittings and loose compression fittings leak. Use brass or stainless steel, tighten connections properly, and check for drips after pressurizing the system.

Frozen pipes in winter: Insulation and winterization aren't optional in cold climates. Prep before the temperature drops, or budget for repairs when pipes freeze.

No water level visibility: You should always know how much water is in your fresh tank and gray tank. Install dipsticks or sensors. Guessing leads to empty tanks and overfull dumps.

Poor ventilation on heaters: Propane heaters and tankless units need proper exhaust venting. Improper venting can create carbon monoxide risk and heater failure. Have a pro check this.

When Should You Plan Plumbing in a Van Build?

Plumbing design isn't afterthought work. It needs to happen early, alongside electrical and insulation planning.

First, decide your water needs: tank size, number of fixtures, toilet style. This determines tank placement and pump sizing. Second, route all lines before you frame or insulate. You need access to run lines and fittings. Third, test the system under pressure before sealing walls. A small leak discovered during testing is a five-minute fix. The same leak discovered months later after walls are closed is a disaster.

We pressure-test all plumbing at 40 PSI and look for any drips over a 15-minute period. Nothing leaks. No water ever gets inside the build.

One more thing: document everything. Label tanks, note the location of every fitting, photograph the system before walls close. When something breaks on the road and you need to find the isolation valve in the dark, you'll be grateful for those notes.