Ensuring clean, safe and palatable
water in your motorhome.

This is a working draft for discussion.

This page is written by an ordinary motorcaravaner who is not an expert on the science of water purity or water cleansing. The reader should not rely solely upon the information on this page. Rather they should use it as one starting point for consideration of the issues and should make their own judgements.

I would welcome criticism, comments and additions. In particular, I would welcome the comments of scientists and water engineers and others who have professional expertise in this field.

If you have experience of using any of the products mentioned in the table which accompanies this article, do tell me about it.

Les Brook 7th November 2000.

Touring with a motorhome, especially in out of the way places, makes one very conscious of the (literally) vital importance of water. We are planning a trip to China and that makes you super-conscious and focuses the mind on how to ensure that your water supply is wholesome.

Design Considerations.

Before deciding what is right for you, some key questions must be addressed.

Where are you going? Which pollutants are you going to encounter? What level of risk do they pose? Do you need to cleanse all your water or only some of it? Is your principal (or even sole) concern a supply of excellent drinking water?

The answers you give may mean that some of what follows will not be relevant to you. Your journeys may be confined to western Europe with its high quality water - in which case you are unlikely to travel down the road of sophisticated filters.

But even in eastern and southern Europe, you may also conclude that the risk is negligible and that you can afford to focus your efforts entirely on maintaining a supply of safe drinking water. Your system could then be as simple as purchasing bottled water! Why do more if it is unnecessary?

Objectives - and the nature of the enemy.

Wherever you travel, the primary objective must be to ensure that all your water is clean and safe but an important secondary objective (not always unrelated to the first) is to ensure that drinking water is palatable. To make water clean, safe and palatable, four types of pollutants need to be addressed:

  • Suspended materials such as sand, rust etc.
  • Impurities causing unpleasant tastes and smells
  • Toxins such as pesticides and those produced by algae
  • Harmful micro-organisms.

What is in the water?

Abridged from Cotswold Outdoor

Only 0.8% of the world's water is usable and safe to drink. Yet 80% of the world's diseases are waterborne.

That crystal clear mountain stream may look refreshing and tempting to drink, but if we examine what could potentially be contained within the water we may think again.

Protozoa are single-cell parasitic microorganisms, varying in size between 10 and 100 microns. They are the cause of the majority of water-related illnesses, spread by humans and animals. The most common is Giardia Lamblia, which attaches itself to the wall of the intestines, effects the digestive system and can make you seriously ill. Protozoa also exist in cyst form with a protective shell making them highly resistant to iodine and therefore removable only by purification and filtration. Examples include Cryptosporidium and Giardia Lamblia. [See here for more info on these]

Bacteria are also single-cell microorganisms normally between 0.5 and 1.5 microns, but can reach a maximum of 10 microns. Also spread by both humans and animals, causing a variety of nasty illnesses from simple stomach upsets to Typhoid. Bacteria can be removed from the water with proper treatment. Examples include typhoid, salmonella, E.Coli, dysentery and cholera.

Viruses are the smallest of the microorganisms found in the water, varying in size from 0.004 to 0.1 microns. They are, however the most dangerous, causing life-threatening diseases such as Polio and Hepatitis. Viruses can pass through even small filters that retain Protozoa and Bacteria. They are most likely to occur in areas of high human contact and particularly in under developed countries. Examples include hepatitis A, poliomyelitis and yellow fever.

Chemicals such as pesticides, insecticides and asbestos can also be found in the water, which causes concern for both long and short-term health. Only certain water filters and purifiers can be relied on to remove chemicals from the water.

Dirt and sediment are present in most water sources, it is easily removed by using a filter or a pre-filter. Boiling and chemical treatments such as iodine and chlorine will not remove these particles. Dirt and sediment particles cause aesthetic problems as well as foul tastes and odours that make the water taste and look bad.

Prevention is better than cure.

What methods are at our disposal to deal with these pollutants?

Our first actions must surely be focused on the water we take on board and the tank in which we store it.

  1. The tank itself must be clean before you embark on each journey. This is easily and cheaply achieved through the use of one or more chemicals - bleach (e.g. Milton), sodium metabisulphate (available from home brewing shops), and proprietary cleansers (e.g. Puriclean [sodium dichloroisocyanurate]). The tank is a potential breeding ground for all kinds of nasties: keeping it clean is simply essential.
  2. Make sure the means by which you fill the tank are right for the job and clean. Use a food-grade hosepipe. Ensure it is clean when you start out and keep it clean.
  3. Avoid taking on polluted water whenever possible. Unless one has some scientific knowledge and/or a water testing kit (are there any that can be used by the ordinary person?) common sense has to be applied - take water from taps marked 'potable' wherever you can and avoid sources that are obviously smelly or dirty.
  4. Filter the water before it gets in to the tank. As I said earlier, the tank is a potential breeding ground for all kinds of nasties and the cleaner the water taken on board, the better the prospects of keeping them under control. But rigging up a pre-filter is easier said than done. I haven't found one on the market, though Whale sell an in-line strainer. This only takes out larger particles of suspended material, but any system that did more than this would have one obvious disadvantage: filling your tank would be much slower.

Clean and safe water storage

Just because we have been careful does not mean the water is now OK, nor that it will stay OK. Whilst the water is in the tank, there is obvious value in cleansing it. Any micro-organisms killed at this stage will not 'reproduce' whilst we are waiting to draw the water off. And some of them may require a longer period of treatment rather than the short sharp shock which is characteristic of cleansing at a later stage, en route to the tap and your mouth.

Elimination of all micro-organisms in the tank may not be possible, but do not underestimate the value of reducing their number. Think about how they 'reproduce'. The cells divide, so 1 becomes 2, 2 become 4 and so on. By the 16th stage, the number reaches 65,536 and by the 32nd stage 4,294,967,296!

The human body is more than capable of handling a wide range of invaders including some of the most dangerous. But when they come in large numbers, the body may be overwhelmed. Fewer organisms in your water mean you have a much better chance of avoiding illness or worse.

If this is not convincing enough, consider this too. Some micro-organisms produce toxins. Fewer organisms mean fewer toxins to be taken out later.

Three 'in-tank' water cleansing methods are available:

Chemicals: most chemical cleansers are variants of chlorine. We can introduce these into the water and they will have a beneficial impact just as they do in swimming pools. These chemicals are relatively cheap. Their disadvantages are that they themselves may pollute the water (most obviously with unpleasant tastes and smells) and they may not by themselves guarantee healthy water if they are ineffective against toxins and some of the most noxious bacteria. However chlorine (the basis of most off-the-shelf product in the UK) will kill most of the water-borne bugs you get in Western Europe, and at least one of these products, Aquasol, claims to kill bacteria and viruses and to remove tastes and odours. Iodine can also be used to treat water and it more powerful than chlorine. It will kill giardia. Unfortunately it can taste pretty bad and long-term use (>1 year) can lead to thyroid problems.

A relatively new product in this class is Sanogene® (based on chlorine dioxide in a two-part sachet.) Each sachet treats 100 litres of drinking water and can be used at higher concentrations to remove "biofilm" (or slime as we call it) from the fresh water tank. (2009-05-26 Unfortunately this product is no longer available. However Accepta in the UK produce chlorine dioxide tablets.)

Ultraviolet Energy: lamps can be purchased which are designed to operate underwater and their light kills all micro-organisms it contacts. This is very good news but the disadvantages of this technology are significant in the motorhome. The costs are considerable, not only of the initial installation but also the replacement lamps that last a year or 8,000 hours. In the industrial situation where they are mainly used, they are kept on all the time which is probably unnecessary in the vanning context but constant on/off switching shortens the life of the lamp. And then there's the fuel consumption, always an issue when relying on a couple of leisure batteries. Finally, it's important to keep the lamp clean which means ensuring any really dirty water is pre-filtered before it comes into contact with the lamp.

Active ceramics: this technology involves suspending in the tank a container filled with ceramic spheres. Remarkably this is claimed to create a myriad of small, localised electrolytic cells which in turn results in the pH of the water rising slightly but significantly. The water is now a hostile environment for bacteria. This effect is supported by infrared light emissions from the ceramic. The technology seems to have many significant advantages. The water is not tainted in any way. The treatment is very long lasting: each unit lasts for five years and works for every minute of every day for that time. The unit is maintenance free. The cost of a unit ranges from £1.40 per litre of tank capacity/£6.50 per gallon of tank capacity (for smaller tanks of 70 litres/15 gallons) to 83p/£3.75 (for larger tanks of 200 litres/44 gallons). The disadvantages are that the technology does not address particle pollution nor toxins, though in killing micro-organisms it prevents some toxins from being produced in the first instance. At the time of writing the claims for its effectiveness do not appear to be supported by independent testing - see caveat emptor below.

En route to the tap.

Most commonly in the motorcaravan context, water is treated in-line on the way to the tap. A permeable barrier is introduced into the pipework that filters out various pollutants.

This is an approach that, to a very significant extent, shuts the door when the horse has bolted. Effective pre-tank or in-tank action seems to offer more than 'doing the business' at this point. (Having said that, a combination of pre-tank, in-tank, and in-line action may well give the best result of all)

Many filters are available that claim to have a beneficial effect and they have the very significant advantage that they allow us to target the water to be cleansed. Depending where we place the in-line filter, we can target the drinking water only, or all water to the kitchen, or every drop of water we use including that for the bathroom. Judicious pipework design could also enable us to vary the water to be treated depending upon the area in which we are travelling.

The products on the market can be divided into two types: simple water filters and water purifiers.

Simple water filters are cheap (though over time the cost may be significant as they have to be replaced regularly) and use carbon (sometimes with silver) to sieve out pollutants. They appear particularly useful in dealing with larger particles and unpleasant smells and tastes. The price of a unit can be as little as £15. Their use means a reduction in water flow but their major disadvantages are much more important than that. They can themselves act as a breeding ground for the very bugs you are trying to kill off and that is why silver is an important component of the better filters as it inhibits this dangerous process. More worryingly, water filters cannot catch the most noxious micro-organisms which quite literally slip through the net. These filters may give the traveller a sense of security which is entirely misplaced.

Water purifiers are also filters which sieve out pollutants but their capacity to catch some of the very smallest and most dangerous bacteria sets them apart from the simpler water filters. Filters operating at 0.22 microns in micro-biological research laboratories are considered to produce sterile water, and a number of products available to the traveller confidently claim to catch everything 0.4-0.5 micros in size with a couple doing even better than that.

So purifiers are designed to deliver safe water and not simply superficially acceptable water. Some of the products are very sophisticated and in one case (the Filopur) both highly flexible and capable of targeting specific pollutants such as nitrates.

The disadvantages of water purifiers are that they slow down water flow (in general to a greater extent than the 'wider mesh' filters) and that they are expensive.

Caveat emptor!

Understandably, most motorcaravaners will have little knowledge of the potential dangers lurking in their water or of the technologies that can be used to deal with them.

In such a situation, it's easy for us to be hoodwinked by glib generalisations and high-flown, apparently scientific, terminology. This is not helped by the apparent absence (in the UK at least) of standards that must be met and against which performance can be judged. Manufacturers can state that their water treatment "kills bacteria and viruses" without specifying which bacteria and viruses, what percentage reduction is achieved etc.

Some manufacturers are very honest. Aqua-filter say their product "is not a water purifier", but other products which appear to have a similar performance are not clear about this crucial limitation. Everpure say "Do not use [the 4C filter] where the water is microbiologically unsafe, or with waters of unknown quality, without adequate disinfection before or after the unit".

At least three manufacturers (Nature Pure, Filopur and Eversure) offer the buyer very full scientific information about what their products do and the standards they meet. Most others do not.

Some manufacturers produce material which is less than convincing. This comment applies particularly to 'active ceramics'. This technology is unusual yet no information is given to support the (very general but grand) claims regarding effectiveness.

From the tap to the mouth!

If you are now confident that the water emerging from the tap is clean, safe and palatable, worry no more.

But you may think further measures are necessary, especially if the water is to be drunk or may be ingested through teeth cleaning, food preparation etc. These further measures are boiling and chemical sterilisation.

Boiling water is an exceptionally efficient means of killing harmful bacteria, the very beasts that filters and purifiers find most difficulty in destroying. It is simple for small quantities though not quick: one 'expert' advises 15 minutes plus one minute for every 1,000 feet above sea level. In a motorcaravan however, boiling has serious disadvantages. It uses valuable fuel resources and creates heat and steam.

Chemicals such as Aquatabs take a little longer to work, but larger quantities can be processed and the cost is not great since only drinking water is being targeted.

In conclusion.

There is no single ideal system. The one you choose should reflect your own carefully considered circumstances. A minimal approach involving regular tank cleaning, filling up with water known to be safe, and maintaining a separate supply of drinking water may be just the job.

On the other hand, in countries where the water is known to be a major source of disease, it seems likely that even the use of a single, expensive and sexy appliance such as the Nature Pure is unlikely to be enough. Special care is required in selecting the water to be taken on board (assuming there is a choice of course!). Pre-filtering of the water is highly desirable with some form of in-tank cleansing so that the water coming to the almost-obligatory in-line filter is already more acceptable than the water you put in the tank.

And if then you still have concerns, a belt and braces approach would require boiling or sterilisation of all water that will be consumed - or you may simply avoid this problem by sticking to bottled water for drinking and using your tap water for such things as washing and flushing.

A simple alternative to bottled water is to maintain your own bottle(s) of purified water. This has a number of advantages. It's cheap and, if you have a few gallons available, means that you can survive disaster striking your main tank supply.



Claims to

Unit Price
(incl first cartridge)

Time / Price.




Sterilising powder.

"Kills bacteria and viruses", "removes tastes and odours"


Not applicable

Widely available in caravan shops in UK. Sterilises 625 litres/142 gallons. Active ingredient chlorine dioxide. Cleans tanks, purifies water in tanks, and veg.

Clean Tabs Ltd., Chichester PO20 6PW


Sterilising tablets


£4.79 for 32 tablets

Not applicable

Widely available in caravan shops in UK. One tab to 22 litres/5 gallons. Active ingredient sodium dichloroisocyanurate. Purifies small quantities of water and veg

Clean Tabs Ltd., Chichester PO20 6PW



I have no information on iodine products



Two part sachet.


£42 for 20 sachets.

  Based on chlorine dioxide. Approved by the US EPA as a water systems disinfectant and water treatment for stored water on board "boats, R.V.s, aircraft, oil rigs, etc." 

(2009-05-26 Unfortunately this product is no longer available. However Accepta in the UK produce chlorine dioxide tablets.



In-line carbon/silver filter

"nasty tastes and smells"

£15.23 plus water system fittings

Replace completely after one season/ 4,500 litres /1,000 gallons

Widely available in UK through caravan shops

Munster Simms Engineering Ltd. Old Belfast Road, Bangor, N Ireland UK +44 (0)1247 270531

CARVER CRYSTAL Carver and Co. Ltd. UK

In-line carbon filter

"odours" "improves the taste of incoming water"


After 4,500 litres/1,000 gallons. £7.95 (but see FILTAPAC below)

Widely available in UK through caravan shops.

Carver and Co. Ltd., Coppice Side Industrial Estate, Brownhills, Walsall UK WS8 7ES (July 2000 - taken over by Truma)


Replacement charge of carbon


Refill only

£3.99 incl p&p

Fits Carver Crystal filter. Very efficient mail order service. Goods will not be despatched until cheque received.

FILTAPAC , 8 Tudor Close, Stone, Staffs UK ST15 OJY +44 (0)1785 816507


In-line carbon filter



Replace annually/ 90 days use

Mail order - see above.

Mail order - see above.


In-line carbon/silver filter

"chlorine, unpleasant smells, tastes and colours …Aqua-Filter is not a water purifier"

£33.31 including filter head

"Annually or sooner". £16.91

Has pre-filter. 200g of carbon/silver. Flows at 14 litres per minute Buy from distributors

ITT Jabsco, Bingley Rd., Hoddesdon EN11 OBU, UK +44 (0)1992 450145

AQUA-SUREBW Technologies Ltd. UK

In-line (carbon/silver?) filter

"unwanted chemicals, odours and particles"

£79.99 incl faucet , piping and p&p

"Every 6 months", £30

Available by mail order

BW Technologies Ltd., Abbey Business Park, Monks Walk, Farnham, Surrey UK GU9 8HT +44 (0) 8705 820 000 contact@bwtechnologies.com


In-line carbon filter

"reduces unpleasant taste and odour"


£8.25 (only available in two pack)

Also available: wall mounting bracket (£11.25) and faucet (complete kit including filter, £41.95)

ABP Accessories, 33 Cannock Street, Leicester LE4 9HR +44 (0) 116 276 9921



In-line (carbon?) filter Details here are for the more powerful 4C unit and cartridge. Also available with standard filter (AC) which is cheaper.

"the taste and odour of ..chlorine …dirt, rust, … asbestos fibre, and oxidised iron, manganese, sulphide… protozoan cysts (Giardia…and Cryptosporidium) …common earthy, mouldy, fishy tastes and odours"

£53.70 for 4C unit.Price excludes VAT and delivery.

Certified for chlorine reduction for 3000 gallons/11,350 litres.£26.10 for 4C model. £22.60 for AC model.

Flow rate 0.5 gall or 1.9 litres /minute.Everpure advise you do not use this product without "adequate disinfection" of the water either before or after the unit.

Ward 0800 854 797 +44 (0) 1799 540983 (Kay Phillips-Anstell Mick Ward) info@watersofteners-filters.co.uk

NATURE PURE General Ecology Ltd. USA

In-line (carbon/silver?) filter

"all microorganisms …specific chemicals, viruses, foul tastes, colours, odours and lead". "Particle retention (nominal) 0.1 microns, (absolute) 0.4 microns"

£90.43 (model 400043 or 400005) incl faucet vessel and piping

Every 500 gallons (2,000 litres). £36

Also available without piping/faucet (model 400007). Flows at 1.9 litres per minute Price quoted is from Associated Chemists (Wicker) Ltd. +44 (0)114 272 7676

General Ecology Europe Ltd., St Andrew's House, 26 Brighton Road, Crawley RH10 6AA UK +44 (0) 1293 539022

FILOPUR Filopur Switzerland
NOTE: All prices exclude VAT (but Swiss VAT is not applicable to goods supplied abroad).

In-line carbon/silver filter

Particles, chlorine, colours, bacteria, viruses, solvents, hydrocarbons, oils - but see comments."Pore fineness of up to 0.4 microns". "…complete elimination of pathogenic bacteria, protozoa and fungus germs".

Approx £83 incl faucet , standard filter holder and piping. Approx £124 for exceptional conditions unit.

"2,000 litres" "average of approximately 6 months" every 4 months in case of extremely poor water. Standard filter £12


Cartridge normally sits on wall behind tap but under-sink version available (kit £57). Automatically clogs when filter needs replacing. Special filters available- std with pre-filter (£13) / nitrates (£36 but can be regenerated) / exceptional conditions (£30). The last two are used in tandem with std filter. They require bigger closure ring on holder (extra £12). Special filters last 4 times longer than std.

Filopur AG, Seestrasse 83, CH-8700, Kusnacht-Zurich, Switzerland +41 1 910 94 03
The products can be bought directly from Switzerland or through Narbonne Accessoires (France)



Immersible active ceramic water cleanser

"constant protection from legionella and other bacteria and micro-organisms"

£98-£165 depending on size of tank (70-200 litres)

Up to 5 years. £98-£165 depending on size of tank (70-200 litres)

Suspended in water tank. Operates by creating electrolytic cells which in turn oxidise bacteria. Needs no maintenance.

KK Water Purification Ltd, Victory House, Victory Park Road, Addlestone, Surrey KT15 2AX+44 (0) 1932 852423

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