Onboard water tank

Hi guys, 
I have just finished sanitising my water system with Puriclean. Having never had an onboard water tank before my question is should I drain the tank and refill it before each trip or is it safe to leave the tank full?
I suspect that I will only be using the van once every 4-6 weeks.

I drain mine every time it gets back home, and refill it day of departure, I also leave the drain hose cock open and hose hanging down.

My van has a sticker from AS which states that water left in system for any extended length of time may become unsuitable for drinking or washing. Therefore I drain down after every trip unless its only 2 or 3 days before going off in van again.

You say 'onboard water tank', but on the Warwick Duo both fresh water and grey water tanks are underslung.  As such, particularly in cold weather it is better to empty when not in use.

We drain down completely (including hot water) after every trip, and if you are only using it every 4-6 weeks this is what I would recommend.

Regards,

Drain down completely at the end of every trip, summer and winter.  I do this on the way home as we leave our last site.

Looks like I’m in the minority, I rarely drain down unless the van has not been used for a couple of weeks which is rare in summer. I don’t use my van in the colder months but if I did then I would definitely drain after every trip. I don’t drink it however, I use a couple of 2L containers for drinking water.
Doesn’t seem to have done me any harm although some would disagree with that!!

Be aware, however, that it is illegal to discharge water on to the highway.

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Hmm. 
I owned cruising boats for 30 odd years which all had fresh water tanks. Draining them down was obviously not an option. I never treated the tanks and never had any problems. Coming onto dry land, we've owned campervans for 17 years now and only drain the fresh water down if there's freezing in the forecast. Despite the recommendations of many, I'm quite happy to drink whatever there is in the tank, however long it's been there and we've certainly never come to any harm.

Hmm.
I am or rather was an offshore sailor.  Whenever I took over a yacht I drained the freshwater tanks and refilled with fresh and always carried bottled water for drinking.  You can’t be too careful on a yacht as if one person goes down with a stomach bug, everyone is likely to go down which is a significant safety risk.  You certainly can’t trust hoses on a yacht which are likely to have been dunked in foul harbour water.

My barge carries 4000 litres of water in galvanised tanks which have never been specifically drained or treated in the 40 years since I made them. The water is fine.

However, we don’t have open vents in the tanks which are exposed to road spray, and we don’t have plastic tanks which can possibly leach chemicals into the water. The MH has both of these issues. So I do tend to drain the MH tank regularly, and run the hose into it whilst draining to hopefully wash out any road nasties. It is hardly wasteful with only a 70 litre tank!

I always use my own hose to fill.