DIY Campervan Water Tanks for Van Conversions

Graham Bogie

Campervan water tanks are central to a campervan conversion’s water system.

They provide a means to store fresh water, collect waste water from showering and washing up and even waste from your toilet.

The entire plumbing system needs to be built around them, so choosing the right tanks for your lifestyle at the design stage is crucial.

There are a variety of solutions for the different types of water storage. In this post, we’ll look at the different types of RV water tanks and things to consider when designing your campervan’s water system.

We’ll also provide a complete parts list for the different water tanks and show how to assemble them when fitting the tanks.

So, let’s get right into it with the different types of campervan water tanks.

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There are three types of water tanks within a campervan:

  1. Fresh water tanks – essential for storing clean, drinking water.
  2. Grey water tanks – collects waste waters from sinks and showers.
  3. Black water tanks – store sewage waste from onboard flush toilets.

Fresh Water Tanks

Fresh water tanks allow you to store usable water in your camper. 

You’ll use water for drinking, showering, washing up and even laundry. There are a few things to consider when choosing suitable fresh water tanks for your lifestyle.

Types of Fresh Water Tank

There are various types of fresh water tanks available, so finding a solution for the limited space in your camper shouldn’t be too difficult.

Portable Water Tanks

types of portable water tanks for camper and RVs

Portable water tanks provide a simple, low-cost solution to carrying water in your camper.

There’s no need to park your van near the water source because you can carry the tank to the fill point.

If your water consumption is low or you don’t use your camper full-time, portable tanks are a worthy solution. Jerry cans and collapsible water tanks are ideal for relatively small quantities.

There are some downsides, though. Hauling full portable tanks around involves some heavy lifting. 

Some portable tanks have integrated wheels to help make it easier, but you may still need to lift the tank in and out of your van.

Portable tanks tend to be much smaller than fixed tanks, so how much water you can carry onboard is limited. It means you’ll need to refill more frequently too.

We think portable water tanks are the best option for short trips, or if you don’t use a lot of water in your van.

Fixed Water Tanks

Fixed water tanks provide a more permanent plumbing solution, so they are best for campervan conversions.

You can install large tanks and expand capacity with extra tanks later too.

There are many configurations of fixed tanks available so that you can find suitable sizes for the nooks and crannies. 

Wheel arch water tanks provide a creative way of using the awkward indoor space at the back of your camper. And by installing one on either side, you can balance the weight (more on that below).

If you’d rather not use the precious onboard space, underslung tanks are ideal.

Fixed tanks are more expensive than portable containers, but they provide a better solution, especially for long term van living.

How Much Water to Carry

How much water you need to carry depends on how many days you want to live off-grid without replenishing supplies.

To work out your daily use, consider how you’ll use water in your camper.

You’ll drink an average of 2 litres per day, each. More if you live in a hot climate.

If you have an onboard shower, you’ll use at least 12 litres per shower, and that’s being quite conservative.

Cooking and washing up uses more water. We use around 7 litres per day between the 2 of us.

Flushing toilets, washing machines and washing sports equipment or pets will use a lot more water too.

As an indication, when we’re frugal with our water consumption, we use about 25 litres per day between us. We don’t use our water system for laundry or the toilet, but we cook and shower from our supply.

Fresh Water Tank Size 

Water takes up a fair amount of space. 100 litres of water needs 0.1 cubic metres of storage, so you’ll need to get creative with where to fit the tanks.

Water tanks are sized in capacity as well as their overall dimensions. Fortunately, they are available in many different shapes and sizes.

There are a remarkable number of spaces under a van to fit a water tank. Look for spaces around and between the chassis rails.

You can even get tanks to fit in the spare wheel stowage. Just move your spare wheel to the rear door.

If you need a large water tank, make sure to buy a tank with internal baffles. They act as water breaks to reduce how much the water splashes around while you’re driving. 

But your fresh water doesn’t need to be carried in a single tank. If you have a couple of available spaces in or under your camper, consider installing multiple water tanks that, combined, provide enough storage capacity.

We have two fresh water tanks on our Sprinter van conversion, three if we count the hot water tank.

water levels balance out when you install multiple tanks

Water Storage & Access

You need to decide if you’ll fit your tanks inside or outside. 

Outside tanks are great for saving indoor space. But if you expect to spend much time in sub-zero temperatures, they could freeze. Not the best scenario to be in. 

Our tanks are underslung, and we’ve lived in our van in winter, through sub-zero winters, without freezing the plumbing system. 

Sure, we needed to do things to protect the system, but to be honest, it was worth the extra indoor space we saved.

If you’re so inclined, you could fit a tank inside and outside and get the best of both worlds. 

Then you can winterise the underslung tank in cold climates and rely solely on the indoor tank. It will require some redirection of the pump’s plumbing, but you can design it for ease of use.

When designing your camper’s plumbing and where to fit the water tanks, make sure to leave access for filling.

We cut a hole in the side of our van and installed a filler fitting. It means we can fill the water tanks from outside without leaving the doors open.

You could install the tanks to fill them directly from inside the van, preferably near a door.

We’ve often found fill points to replenish our water supply but with no hose attachments. Now we carry a garden hose and a range of Camco water bandit stored in our engine bay, so never have a problem.

Access is also needed to drain the water tanks for storage and cleaning.


Weighing in at 1 kilogram per litre, or 3.785 lbs per US gallon, water is heavy. The amount of water you can safely carry is limited not to exceed the legal limit of your vehicle’s weight.

Even keeping within those restrictions, a large, full water tank will negatively affect fuel consumption, speed and the vehicle’s handling.

If you’re building a camper for long term overlanding, we recommend reading our post on modifying your overland build

In summary, though, the handling becomes less predictable with more weight and makes the camper less capable off-road. 

If possible, position the water tanks:

  • low to the ground, to keep the centre of gravity as low as possible,
  • between the two axles, to share the load equally across both axles and suspension, and
  • spread evenly along the centre line of the vehicle to help stability on extreme terrain.


Most fresh water tanks for campers are made from food-grade plastic like polyethylene. Look for seamless tanks as they help prevent algae growth that can cause a bad taste.

Stainless steel tanks would prevent any algae problems, but they’re more difficult to source and expensive too.

We have plastic tanks and have lived in our van full-time for over three years and never had a problem. We occasionally flush through with a mild solution of household bleach to keep the tanks in tip-top condition.

Parts of a Fresh Water Tank

Off-the-shelf fixed water tanks include four holes, each crucial to the correct operating of the tanks. 

If you buy a custom tank, ask for four holes positioned where you want them. If in doubt, drill the holes yourself so you can position them perfectly for your conversion.

parts of a campervan water tank

The filler port is obviously where you’ll fill the tank. How you connect the water hose to the fill line depends on whether you have an external filler or plan to fill it from inside.

The drainage port is positioned at the bottom of the tank and used to empty the tank.

The water pump port is where the internal plumbing connects to the water tank.

The air vent is vital and should be positioned on top of the tank. It’s a one-way valve, so it prevents any debris from entering the tank.

The vent allows air to escape as you fill the tanks. Without a vent, the air can’t escape, and you’ll end up with airlocks. As water is used, air is allowed into the tank via the non-airtight fill lines.

Campervan Water Tank Level Indicator

Running out of freshwater is a bad idea, especially when travelling in remote regions where access to potable water is challenging.

The way we have installed our water tanks means we can’t eyeball the water level. Having a water gauge takes most of the guesswork out of monitoring how full we are. 

Float sensors work by floating on top of the water level, which moves along a 12v resistor, indicating how empty or full the tank is.  

Resistance sensors are more modern than float sensors. Passing milliamps through the water, it measures how full the tank is. Because it uses electronics, the readout can be displayed on an LED reading rather than on a more dated gauge. 

Both types of water tank level indicators need a small electrical supply. You can easily incorporate this into your van’s electrical design.

Float sensor indicating the wtaer level inside the water tanks

Grey Water Tanks

Any campervan water system needs containers for collecting waste water. A grey water tank allows you to collect waste water from your campervan sink and indoor shower.

Some of the same considerations to fitting fresh water tanks apply the waste water tanks too.

Types of Grey Water Tanks

The most straightforward approach is to feed it directly into a jerry can securely stored beneath the sink. 

Make it a different colour to your fresh water can to avoid mixing them up.

diagram of a simple water system for underneath a campervan sink

Portable waste water tanks have wheels making emptying easier. They’re generally positioned outside the van. You’ll need to feed the drainage pipe through the van’s floor and connect a hose each time you set up camp.

Portable grey waste tanks are ideal if you plan to spend most of your time on campgrounds and have somewhere to store the tank while you’re travelling.

They’re not the best option for stealth camping or off-grid living, though.

We fitted a permanent grey water tank to the underside of our camper, and it collects everything that goes down our drain. 

A permanent tank needs to be plumbed once, so there’s no setting up when we arrive on camp. 

Grey Water Tank Size

A waste water tank doesn’t need to be the same size as a freshwater tank.

Firstly, not all the fresh water ends up in the waste. You’ll drink some of it and perhaps use an outdoor shower occasionally.

More significant, though, storing grey water isn’t as crucial as storing your potable water. You can empty your tanks. 

When choosing the best size waste tank for your van, consider how much water you’ll use each day, how much of that is likely to end up in the grey tanks and how often you will be able to empty it.

Make sure it is at least big enough to hold enough water so you can take a shower!

Our grey water tank is 50 litres (about 13 US gallons). We empty it at least every two days, but it’s never filled up completely, so we know we have some spare space if we can’t find responsible drainage anywhere.

Water Storage & Access

external gray water tanks on a campervan

As with the fresh water system, grey water tanks can be installed inside or outside the van.

Because the waste water tank is usually much smaller, it is more likely to freeze in sub-zero temperatures. That’s the last thing you want. 

If you install it outside, take the necessary precautions in cold temperatures to prevent it from freezing.

Wherever you install your grey water tank, take care to ensure easy access for emptying.

Our underslung tank has an access tap just behind the line of the van, so it’s easy to empty. If you choose to install yours inside, make sure you have a screw-on lid to prevent any spillages, and empty it before it’s too heavy to lift.

Where to Dump Grey Water Responsibly

Do you know what happens if you don’t empty your grey water tank before it’s full?

Yep, it’ll back right up into the kitchen sink or shower tray – whichever is closest to the tank. 

Avoid showering in a tray full of your dirty dishwater by emptying it as often as possible.

You can help keep your grey water “clean” with these simple tips:

  • Clean all food debris from your plates and pots before washing them.
  • Use a sink strainer in your shower tray and the kitchen sink to prevent large particles from entering the system. 
  • Use eco-friendly, biodegradable soap wherever possible.
clean as much food waste from your plates to protect your grey water tanks

So where can you dump your grey water? 

Grey water is not necessarily harmless. Bacteria, fats and detergents aren’t what the local flora and fauna would naturally encounter.

To protect our environment, only dump grey water where you know it is safe, responsible, and you have permission.

Depending on where you are, RV dump stations might be commonplace. In Europe, Aires usually have grey water disposal points. 

In the UK…. well, if you’ve tried boondocking in the UK, you know how tough that is!

Even so, campgrounds provide waste disposal points, and many will let you use them, even if you’re not staying there.

If dedicated points aren’t available, don’t just dump your waste wherever you want. There are rules and laws in some places preventing you from doing so. Please make yourself aware of the local regulations and follow them.

In any case, here are a few tips for dumping your grey water responsibly:

  • Always maintain a distance of at least away 100m from any water source.
  • Scatter the waste water across the ground rather than pour it in one spot (we use our trash bin as a bucket for this).
  • Never dump more than 5 or 6 gallons at a time.

Read more about the leave no trace guidance on the Leave No Trace website.

How to Clean a Grey Water Tank

A buildup of food particles and bacteria can lead to unpleasant odours wafting up through water pipe and into the kitchen sink or shower tray.

Keeping the grey water tank in good shape is essential for preventing these bad smells.

Scraping as much waste from plates and pots before you start washing dishes will help. And though it may sound counter-intuitive, the best way to flush the tank is to keep the tap closed until it’s at least half full.

When you open the tap, the whoosh of water flow will help flush out debris. Prevention is better than cure!

There are special grey water tank detergents available, but we think these are unnecessary, to be honest.

A mix of hot water and bio-degradable soap is hard to beat. We live in our van full-time, so we don’t have the benefit of being able to leave the grey water tank in soak for any amount of time.

We clean our grey tank on a day we plan to drive for a few hours. We wait until it’s at least half full and empty it. 

Then we fill our kitchen sink with hot soapy water and remove the plug. We usually do this a couple of times. This creates more substantial water pressure to flush through the water pipes to the grey tank.

As we drive, the clean water sloshes around the grey water tank, and we empty it at the end of the day. It’s usually evident from the colour of the water whether it needs to be done again.

RV Black Water Tank

Emptying an RV black water tank

Some motorhome and RV owners opt for black water tanks to collect human waste. 

There are plenty of campervan toilet options to avoid black tanks altogether. We have a composting toilet and love it!

That aside, it would be remiss of us to write an article about a van build’s water tanks without giving black tanks a mention too. 

Black water tanks are usually installed outside of the van. Permanent tanks fit underneath, and you’ll need to find a suitable size and shape for the available space.

Some RVers use portable black tanks too. They attach to the main onboard black tank allowing contents to pass through. The portable tank can then be wheeled to the dump station and emptied much like a cassette toilet.

This means you don’t have to break camp to empty your main tanks once they’re full. It’s a good idea for RVers who spend a long time on the same campground. 

Dumping black water tanks is, of course, different to emptying the grey water. Only empty them at an authorised dump point. 

sign for an rv dump station

We’ve heard people claiming that the contents of a black tank, when no chemicals are used, is entirely organic, so safe to dump. But stop it, please.

It may well be an organic material, but it is completely irresponsible to dump your crap anywhere you want. Think of other people and their kids encountering it!

And opening the dump valve as you drive along is gross for any car, motorcyclist or bike riders following you. 

In many countries, if you are caught dumping on the road, you will be heavily fined.

RV Hot Water Tank

Separate RV hot water tanks are not essential in a van build. Of course, you can opt for a cold water only set up. This might be a good idea for a short camping trip, but not how we would want to live in our van long term.

A camper’s water heater doesn’t have to rely on separate water tanks. Tankless RV water heaters draw cold water directly from the freshwater tanks, so there’s no need for an extra tank.

We do have a separate hot water tank in our van build. It’s a relatively small 20-litre Elgina coalescer water heater. It allows us to heat water from the engine as we drive and from the 12v system

We’ll write more about the Elgina coalescer and tankless water heaters in future posts.

Tips on Installing Campervan Water Tanks

campervan water tanks installation tips

Regardless of what type of campervan water tanks you fit, they need to be securely installed so they cannot move in any direction.

Underslung tanks need hanging brackets. They shouldn’t interfere with access to the filler port or drainage ports. 

The brackets should be secured to the vehicle’s chassis or other points equally robust. Find a place where cross members or exhaust pipes won’t get in the way either.

underslung campervan water tank brackets

Before buying your tanks, measure at least twice. Cross members have a nasty habit of suddenly appearing when you fit a new tank – at least they did when Graham fitted ours. 

You should also take into account that the advertised size of many plastic tanks is approximate. We had to return two tanks when we ordered ours because they were over 2” bigger than the published size.

To install water tanks inside, you’ll need a robust securing mechanism, preferably secured to the strongest point on the van’s floor or vertical ribs of the van. 

Any securing bolts must be robust enough to cope with the weight of a full tank shifting if there was any sudden breaking or worse, you rolled the vehicle.

Position the air vent and fill port at the top of the tank and the drain port at the bottom. 

The pump port can be positioned at the bottom or the top of the tank. If it’s more convenient for your installation to have the pump port at the top, you’ll need to insert a water pipe riser inside the tank so it draws water from the bottom.

An underslung grey tank doesn’t have to be installed directly underneath the sink. It’s best to position it in whatever space is available where the weight is balanced.

Using large-bore waste pipes, at least 1 inch or 25mm in diameter, will help prevent clogging in the grey water system.

Avoid any bends and kinks when laying the water hoses and pipes to avoid splitting. Use P clips to hold pipes and hoses in place.

Avoid laying any hoses near or over exhaust pipes so they don’t get hot and melt – that is the voice of experience you hear!

Assembly & Parts List

Unlike the parts needed for a campervan electrical setup, plumbing components aren’t standard.

While this article is focused solely on campervan water tanks, you should consider the van plumbing and installation when you’re buying parts.

Most water tanks do not include the assembly parts for the plumbing.

There are at least three different ways to attach pipes to the water tank, depending on how it’s been manufactured. And there’s a multitude of pipe fittings and sizes.

  • NPT or NPS (national pipe tapered or straight): used in North America 
  • MIP or FIP (male or female iron pipe): which is the same as the NPT.
  • BSP(T) or BSP(S): British standard pipe tapered or straight: and mainly used in Europe.
  • Compression: a unique fitting that does not mate with other thread types
  • UNS (National Unified Special): might work with some compression fittings.

Each method requires different parts to attach the hose securely. And to make it even more complicated, hose sizes are non-standard too.

So the parts need to be compatible with the hose size and the water tank connection type and size.

In all likelihood, you’ll end up with a hose size of your choice, one type of connector for the water tank and different connectors to join it to your 12v water pump

Threaded Inlet

Some water tanks have a threaded inlet in each of their ports. It’s a simple connection method. 

how to assemble campervan water tank threaded inlet

Parts needed:


  1. Wind PTFE tape onto the threaded connector (where it inserts into the water tank)- 3 times will be thick enough to prevent leaks but not so thick you can’t screw it into the inlet. Make sure you wind it on in a clockwise direction, so it doesn’t unravel as you screw it in.
  2. Insert the threaded connector into the water tank and screw it on tightly.
  3. Insert the rubber seal into the threaded pipe end.
  4. Wind PTFE tape onto the threaded connector (where it joins the pipe).
  5. Connect the threaded pipe end to the threaded connector. 

Spigot Pipe

Some water tanks are manufactured with an inbuilt pipe or spigot. It protrudes from the tank, ready to attach a hose.

Hose & Clamp Connection

A hose and clamp connection is a simple way to attach a flexible hose to the spigot.

campervan water tanks hose and clamp connection

Parts needed:

  • Flexible hose (compatible with the spigot size)
  • Jubilee clip (compatible with the spigot size plus the thickness of the hose)


  1. Set the jubilee clip over the flexible hose loosely.
  2. Push the hose onto the spigot, as far as it will reach.
  3. Position the jubilee clip around the spigot and tighten.

Compression Connection

Compression connectors work well with water tanks with a spigot. It’s much easier to install than a hose and clamp too.

campervan water tanks compression connection

Parts needed:


  1. Insert the hose into the compression connector and pull back until it bites and the connection is secure.
  2. Set the compression connector onto the spigot and pull it back until it bites and the connection is secure.

Custom Connection

Some water tanks don’t have any pre-drilled ports or if they do, they are straight forward holes without any in-built means of connections.

You can assemble your own connection though so long as you have access to the inside of the tank.

campervan water tank connection

Parts needed:


  1. Drill correct size hole if not pre-drilled.
  2. Put a rubber washer onto the threaded connector.
  3. Wind PTFE tape onto the threaded connector.
  4. Insert the threaded connector into the water tank through the hole you’ve just drilled.
  5. Put a rubber washer onto the threaded connector inside the tank.
  6. Put the nut on and tighten.
  7. Connect the hose to the spigot depending on which type of connector you have selected (compression, jubilee clip etc).

Graham Bogie

Graham Bogie - Expert in RV & Campervan Electrics - Mowgli Adventures

Graham is a seasoned marine electrical engineer with two decades of experience designing customized electrical systems for plant machinery and converting campers and overland vehicles. His expertise has led him to author the reputable Campervan Electrics Handbook and become the chief designer of the RV Wiring Design Tool. As a knowledgeable figure in the field, his YouTube channel, blog, Facebook group, and newsletter, offering electrical advice and product reviews, reach more than a million users each year.

5 thoughts on “DIY Campervan Water Tanks for Van Conversions”

  1. Very confusing.

    “The air vent is vital and should be positioned on top of the tank. It’s a one-way valve, so it prevents any debris from entering the tank.

    The vent allows air to escape as you fill the tanks. It also allows air into the tanks as the water is used. Without a vent, the air can’t escape, and you’ll end up with airlocks.”

    Is it one way or two way?


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