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Water tank treatment

Can you please advise about water tank treatment on my narrow boat.
I do not use my boat from October to April, in October I drain the tank by running it empty. What treatment should I do when I come to use the boat in April, also what about the water hose pipe.

Asked by: David Anderson  | 7.13pm, Wednesday 2 April

WW says:

There are commercial water tank treatment products available to disinfect the tank- however, you can achieve excellent results using cheap THIN bleach (such as "value" range bleaches). Thick bleach contains sodium hydroxide and MUST NOT be used. Thin bleach is around a 5% available chlorine level. Do not be tempted to use anything other than thin bleach!
The following amounts should give you a sufficient disinfection regime:
Amount of 5% chlorine (standard thin bleach) to add for:
Volume to treat 50ppm 100ppm 0.5ppm
100 litres 100ml 200ml 1ml
10 litres 10ml 20ml 0.1ml
100 gallons 450ml 900ml 5ml
10 gallons 45ml 90ml 0.5ml
Add the bleach and fill the tank. Then, starting with the taps closest to the water tank, open them and run, until a smell of chlorine can be detected. Continue with every tap, including any linked to toilets, until all are complete. Then top up the water tank with a chlorine solution, to replace the water used. Leave for at least 4 hours. Then, open taps and drain the tank. By this time, the amount of chlorine will have declined massively, so will not be a great harm discharged overboard, but if you wish you can drain ashore via a hosepipe, which is preferable is you are based on a canal. Refill the tank, and pump through the taps, until a "normal" level if chlorine is smelt. This is important especially in the hot water side of the system.
The initial emptying of the tank really should be done through a hose back ashore, to avoid dumping excess chlorine into the canal/river.
Hosepipes should, at least every 6 months, be filled with a 100ppm chlorine solution (twice the concentration used to sterilise the tank) and left for an hour. After normal water filling, the pipes should be drained and the ends capped, to stop contamination. The connections should be rinsed or wiped with a dilute chlorine solution each and every time it is used. This should prevent the build up of biofilms in the pipe.
Any questions, please let us know.

Mark Langley  | 9.20AM, Thursday 3 April

Apologies that the table I inserted above has not reproduced here!
For a 50ppm chlorine solution, use 100ml thin bleach per 100 litres of water (or 450ml per 100 gallons)
For hosepipes (needing a 100ppm solution) use twice the amount (i.e. 20ml thin bleach per 10 litre bucket)
Hope that makes sense.
The 0.5ppm does level (1ml per 100litre water) is a maintenance dose which can be added to normal water, to ensure sufficient chlorine remains in the tank during use.

Mark Langley  | 9.24AM, Thursday 3 April

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