Simon,
I take it that you now live in a flat
I do as well, a first floor with no outside tap.
now this is only a suggestion but maybe something you've not considered.
This is what I have done
I have connected a hose pipe outside the window nearest my van, cable tied it to the outside of a drain down pipe, either end is hozelock type connecters with taps.
I carry an additional reel of 1/2 " hose that I run from the van to the hose at the bottom of the downpipe and the same with a short length from an inside tap ( a washing machine style self tapping to the mains in the kitchen ) that I connect up outside the window.
The hose feed to the van goes up through the floor behind the rear bumper so is locked and secure.
Seems a shame to waste your investment and be reliant on someone else for pure water
Maybe this is'nt viable for you but maybe it will be of help to someone.
Simon