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Motorhome advice: A beginner's guide to on board water


The joy of motorhoming is in the freedom it provides to explore – you can be self-sufficient in the wildest of spots. But, none of this is possible without the life-sustaining support of fresh water or, as it’s otherwise known, potable water.

Set against the benefits of on-board water you have to consider the negatives of such a system:

  • You must allocate precious payload to allow for the weight of water
  • The processes involved in loading up and disposing of waste
  • Keeping the stored water in a safe, drinkable condition
  • Avoiding possible damage from freezing water in the colder months.

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How does water affect my motorhome's payload?

One litre of water weighs one kilogram (1kg), so a typical 100-litre fresh water tank filled to capacity takes out 100kg of payload. That’s quite a chunk of most motorhome’s payloads, but generally you don’t need to drive around with a full tank and it’s not advisable to do so. Lugging around large amounts of water means you’ll suffer from greater fuel consumption and the sloshing around in a tank without baffles can reduce driving stability.

It’s advisable to check your available payload for what water you can legally carry. The best way to do this is to take your motorhome to a public weighbridge (your local council should be able to point you in the right direction) when fully loaded, excluding water but including driver and passengers. Compare this weight with the permitted gross vehicle weight (GVW) – the top number shown on the plate under the bonnet. The difference between the two weights is your spare payload, assuming your loaded weight is less than the GVW!

Loading and unloading of water to your motorhome

Loading of fresh water and unloading (grey) waste water depends on personal preference and the facilities available. More campsites are providing motorhome service points where you can park adjacent to a fresh water tap and drop your grey water directly into a drain. Super pitches are also becoming popular where each pitch has direct access to water and drainage.

In these situations, the first essential is a length of hose to fill the tank up. Don’t be tempted to use a garden hose as this is likely to taint the water because chemicals can leach out into the water. A food-grade hose uses materials that won’t taint water and will discourage the build-up of biofilm on the pipe walls, but more about biofilm and bacteria later.

For normal pitches a portable jerry can is invaluable. Again, use a container made of food-grade plastic and, although a watering can is convenient for a quick top up, it’s unlikely to be made of food-grade material. It will take four trips to the water tap to fill a 100-litre tank with a 25-litre container, but most people will struggle to manhandle 25kg. So, a large wheeled trolley, preferably collapsible for storage, is a useful accessory for transporting fresh and waste water tanks.

Cylindrical water tanks like the 40-litre Aquaroll are opaque and are ideal for moving and storing a large amount of water over the roughest of ground. However, they are bulky and inefficient to store. Rectangular containers are more suited for small and medium-sized motorhomes with limited storage.

Once you have a large container of water next to your motorhome, trying to lift it to pour water into a filler at waist height is no mean feat. Consider the Whale Superfil kit or make up your own kit with a submersible pump, length of hose and lead to reach your nearest 12V socket. A HEO water filler cap is useful for keeping the hose with a snap-on connector in place during the filling operation. Also useful to carry about with you are a selection of adaptors for making a secure connection at the site supply tap.

For dumping waste water with ease on a campsite super pitch, or for where you can’t park directly over a waste drain, consider carrying a flexible hose. However, more than a couple of metres of semi-rigid hose is rather bulky and can be resistant to uncoiling and lay-flat hoses tend not to open out for unpressurised liquids. A portable waste tank is probably the easiest solution.


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Safe drinking water in your motorhome

Some motorhomers prefer to use bottled water for drinking or filling a small container directly from the site tap and rely on the fact that cooking and tea making involves boiling water, which should kill bacteria. Apart from the current outcry about overuse of plastic bottles, such usage is not so practical when considering safe water requirements for washing food and cleaning teeth. But is there really a need to consider water from your motorhome tank unsafe? What are the risks?

Generally, water should not be used if stored for more than 24 hours as its quality will deteriorate. Within this time period the chlorine put into the water by most public water suppliers to keep it safe will have dissipated and the water will be at risk of being a host to bacteria potentially harmful to health. It doesn’t help if your motorhome water system has been allowed to fester in between trips with stagnant water in the pipes, especially in warm weather.


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A water supply system, which does not have a regular turnover of water, will develop a biofilm on the internal surfaces of pipes and tanks. Added to this it’s likely when using hard water there will be a build-up of limescale in the system, which all adds up to an environment for bacteria to thrive. At this point you may consider selling your unhealthy motorhome but easy-to-use products are readily available to descale and sterilise your system to keep you safe.

  • Descaling — Apart from the hygiene benefits of descaling, Truma recommends descaling the Combi boiler at least twice a year. Filling up the fresh water tank, pipework and hot water boiler with food-grade citric acid in solution in accordance with the manufacturer’s recommendations will dislodge limescale and other debris including biofilm along the pipework. Elsan’s Fresh Water Tank Cleaner combines citric acid with cleaning agents and a product to inhibit the growth of bacteria and is marketed as an all-in-one descaling and sterilising agent
  • Sterilise — Some environmental authorities recommend water systems be sterilised before each trip. Many sterilising agents contain chlorine, which is an effective sterilising substance but it’s corrosive to stainless steel, a material found in many motorhome hot water boilers. Certainly use inexpensive chlorine-based baby sterilising fluids or tablets for your portable and underslung tanks. But do not switch on your pump to lift the sterilising solution into the motorhome pipework system and hence the water boiler. For whole system sterilisation use products produced for the leisure market that clearly state the ingredients do not contain chlorine
  • Additives — If it’s likely you will want to use water stored for more than 24 hours especially in warm weather, consider adding a product like Elsil. Elsan (of toilet fluid fame) claims water treated with its Elsil product will remain drinkable for several weeks. With an increased dosage, Elsil and other products can be used for making water, which is likely to have been contaminated, safe.

External water contamination in motorhomes

Similar cross-contamination can occur when on temporary sites where there are no cassette flushing facilities. On well-run rallies there is normally a sign indicating toilet cassettes shouldn’t be taken near the fresh water tap.

There’s also a risk of contamination from your own accessories like hoses and jerry cans and even from your internal taps. So, when you clean out your motorhome system, don’t forget these accessories need cleaning.

It’s always a good idea if you tend to do all your filling and emptying at the same time, to start with collecting your fresh water supply (with clean hands) and then progressing to grey water disposal and subsequently cassette emptying duty. Regular hand washing and care on how you deal with fresh and waste water should eliminate much risk of contamination at the tap.

Are filters the answer? You are likely to encounter three types of filter in a motorhome but only one can provide safe water:

  1. Activated carbon filter — Carbon filters are designed to remove unpleasant taste and smells. They do not deal with harmful bacteria and, if not replaced at intervals as recommended, they can cause a build-up of bacteria
  2. Grit filter — These filters use a metal screen to strain out grit in the water before it enters the pump. They don’t perform any water quality function, they are needed because diaphragm pumps are susceptible to grit damage. Check and clean the grit screen at least once a year. If left for too long you will get a build-up of bacterial growth
  3. Microbiological purifier — Often found on canal boats, they are ideal for motorhomes. They claim to be able to change virtually any non-salt water into drinking-quality water. You are looking at around £300 for a system with a separate tap plus fitting costs and cartridge replacement costs of around £80. Because the filters will only deal with a set volume of water before needing replacement it is probably best to fit a separate tap rather than pass all the ’van’s water through it to avoid frequent changes of the expensive filter.

Avoiding frost damage in your motorhome's water tank

Sub-zero temperatures are a problem when camping and during winter storage unless preventative measures are taken. The most obvious is to keep the heating on and, if necessary, open up lockers to get heat to pipes in remote places.

An on-board tank or a tank located in a heated sub-floor cavity is best but, if you have the more usual underslung tank, then fit a heater and insulation. Don’t fit insulation without a heater as, given time, the tank will freeze and then the insulation will delay the thawing process.

Waste tanks are best left with the outlet valve open to drain into a portable tank. Last thing at night, pour salty water down the kitchen and bathroom waste to discourage any water trapped in external pipework from freezing on colder nights. Have a small water container that is available for collecting water from indoor taps when all the external campsite taps freeze up.

How to drain your motorhome's water system for winter 

Even a small amount of water has the potential to cause expensive damage when it freezes so effective draining is essential. The recommended drain-down procedure is:

  • Open all taps including the shower and, for mixer taps, ensure the lever is in the central position to allow for both hot and cold to drain. Remove the shower head and empty it of all water
  • Drain the fresh water tank and open the internal drain valve, which is generally situated close to the water heater
  • Run your pump for a few moments to clear it of water. Most good pumps can be run dry for short periods without causing any harm
  • Remove any filters fitted, which may hold residual water. If it is a carbon filter designed to improve taste, retain it for the spring sterilising operation as sterilising solutions can damage such filters
  • Ensure your ancillary water accessories, such as external pumps for filling the tank and portable water containers, are fully drained and permitted to dry out to prevent mould growth
  • Encourage the last drops of water out of your system by driving home from your last stay on site with all the drain valves and taps open. Ensure the bulk of the water is drained out first so only a small residual amount of water is left on-board to avoid creating a danger or nuisance to other road users
  • With the pump off, leave the taps fully open over winter, this will provide room for expansion if any residual water that is left in the tap body freezes
  • If small pockets of water remaining in the system don’t cause damage, such stagnant water doesn’t bode well for the safety and taste of water next season
  • Cassette toilets with a flush water supply tank need to be drained, too. When drained, press the flush button to clear any residual water in the flush tank pump
  • Leave drain valves open to vent your waste and fresh tanks but cover the outlets with mesh to stop insects and other creatures setting up home in your tanks. Finally consider a Floë drain-down system, which makes for easy and very effective removal of residual trapped water in the system using low-pressure air.

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