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A boat’s fresh water system needs annual maintenance to keep it in good condition. Some boats have far more complex systems than others, with pressurised hot and cold water, associated pumps, an accumulator, calorifier and pressure valves, all to keep a boat owner busy. On the other hand, smaller boats usually have unpressurised systems which means they are much less complex, therefore easier to maintain and less to go wrong.

Water system maintenance and troubleshooting

Water pumps tend to be robust devices that are capable of operating for many years without trouble, particularly if there’s a filter in the system ahead of the pump. However, they are not immune from wiring and other electrical supply problems and ultimately have a finite lifespan.

Leaks from a tank, or another part of the system, however, are more commonly found. These can be caused in a number of ways, the most obvious being a flexible tank that wears a hole due to chafe, although even stainless steel tanks have the potential to develop pinholes that can be difficult to track down.

Water tanks

I have to confess that I’m always a bit wary of fresh water tanks on boats. The water is usually fine for boiling a kettle and making tea or coffee, but I like to keep bottled water aboard for drinking and have 5 litre re-usable water carriers for the purpose. I also have a UV Steripen for purifying water on longer trips which is a brilliant way to disinfect water and leaves no after taste.


Fresh water tanks can be made from stainless steel, fibreglass or plastic, some of which are flexible, therefore able to adapt to the shape of hull where they are installed.

Fresh water tanks and all pipework should be cleaned annually, which involves draining down the system and then filling with a water sterilising mixture. I normally use Milton sterilising fluid, best known for sterilising baby bottles but also used by boaters. Add 30ml of fluid per 5 litres of fresh water. Leave for a couple of days, then drain the system again. Then either re-fill with fresh water if the boat is in use or leave the system empty until the boat is returned to the water in the spring.

Other options include adding filters to the water system such as activated carbon filters and sub-micron filters. People also use additives such as Aqua Clean or even lemon juice.

Contaminated water system

If a water system has become severely contaminated then the time may have come to replace all the pipes and possibly the tank as well. Pipes can become contaminated with very unpleasant fungal or algal growth which can be harmful to health. Making a decision is up to the individual boat owner, but if things get that bad and the regular sterilising and system cleaning has been forgotten or has not worked, then I would choose to replace the contaminated pipes. Your boatyard manager should be able to advise on the best course of action.

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