Keeping Undercamper water tanks sterile.

Opinions vary. I prefer to store mine full on the basis there is less air to help the nasties breathe and grow.

Every trip I drain and re-fill with fresh water.

Every 6 months I sanitise the system with 1:1000 chlorine bleach. eg 50ml laundry bleach in 50 litres water. Run it through the taps and pumps until you can smell the chlorine, leave for 12 hours, then drain, flush tanks and pipes/pumps and re-fill.

Cheers

The clear plastic overflow pipes are a problem. Mould needs light to grow. Exclude the light by using black tubing and that will fix that problem.
In the 8 years I have had my van I have never treated the tanks. Most times I just park up with whatever is in the tanks and fill them when heading off next time. I must say I have never had the water tested or suffered ill effects.

I do a similar thing to frank except I use a comercial drinking water chlorine treatment and leave it in the full tank. My van has black tubing so no trouble with mould.

Hi All
Thanks your thoughts on my issue.I think I'll use Frank's chlorine dose to hopefully kill the mold and store the tanks full.I wonder if spraying all the visable clear tubing with black paint would help?I'm thinking it can't hurt to give it a try.Thanks again.
Regards Ando

Mold can grow happily in the dark. It is algae that needs light. Algae can grow in damp areas or under water, mold just likes it warm and damp. Black tubing just means you can't see the mold.

If you can't pump it completely dry, then probably best to leave it full and dosed with something to inhibit the growth of gunk. I used to use a home brewers bottle sterilizing solution which was basically sodium percarbonate (nappysan is around 20% sodium percarbonate). The water always tasted as fresh as the stuff straight out of the tanks at home.

Hi ANDO

Although storing with them full would be better, we leave them as they are when we get home, and top them up before going away, even with years between trips. After all the water is more sealed from the light than in the household rainwater tank which also gets topped up, each winter and we have to manage so it never gets empty.

We only fill with town scheme water or clean water. Anything with obvious sediment gets used direct from a bucket rather than through the tanks.

Yes, clear hoses are not a good idea. We use black irrigation trickle pipe for the breathers. If you have clear hoses for delivery and they collects algae, it is cheap enough to change periodically rather than try and clean them all. These drinking water quality hoses are available from Bunnings. Otherwise replace with with the more expensive lined food grade hoses.

Couple of points to consider.

Remote area houses have used tank water for years and don't drain them except for maintenance. Same idea as your camper.

I never emptied mine either until one day whilst swapping out a toilet cistern (town chlorinated water) I noticed a film of slime around the inside of the cistern. Not the green type of thing, in fact not visible but you can certainly feel it with your hand.
That water is turned over several times a day and is stored without sunlight yet something grows.

Started draining my tanks for long periods of disuse after that. Also makes the trailer lighter to tow on the home leg.
If I do any sterialising of anything, I use Milton baby bottle cleaner. Tastes better than chlorine or bleach.

This paper compares sodium hypochlorite (liquid chlorine bleach, Milton liquid) with sodium dichloroisocyanuric acid (slow release pool chlorine, Milton tablets, various trade names) for household water treatment.
http://www.unicef.org/cholera/Annexes/Supporting_Resources/Annex_9/Clasen-NaDCC2.pdf
If you skim over the chemistry and tech bits you'll be able to get the gist of it. Advantages of milton tablets is that it's slow release and the tablets have a shelf life of several years whereas the liquid sterilising solutions gradually loose chlorine and efficacy.