I have 3 five gallon plastic Jerry's for my own Van. Of course I can fill them at home before taking off, but once the water is used and the jugs need to be refilled the sources along the way may be questionable.
Those 0.5 micron filters that compasrose speaks of are what I use in my own home and I get them at Rural King for a dollar each.
I found a home filter canister in a yard sale that they were disposing of as they had installed a water softener. Got if for a couple of dollars. I've also found a Pur faucet end filter that I'm wanting to use as a second stage.
Faucet end water filter Charcoal
10 ft piece of Marine hose.
I figure on using the hose connected to the canister 0.5 micron filter from the hose bib (somewhere).
The filter will be connected to the Pur faucet end filter (as a second stage) via a piece of hose with the proper adapters at each end.
At the hose bib I'd be using I'd use an inexpensive "ball" shut off valve.
It is important to follow the directions when using a new charcoal filter in the Pur filter as the water has to be turned on and the filter become wet. They suggest allowing water to run through it slowly for 15 minutes
to thoroughly activate the filter cartridge and flush it out before drinking water from it.
But I figure this kit (the two filters joined by the adapter hose) could be stored in a 2 gallon zip lock bag and that in a small plastic bin large enough to hold it. The Marine hose and ball valve could stow elsewhere.
What I figured on doing was stopping by various Gas Stations when I need fuel and ask the attendant if I could purchase a few gallons of water from him. (usually they will just tell you to get what you need so long
as you aren't filling a 50 gallon tank) But with this kit I figure I could get reasonably safe water that would
not have an objectionable taste or smell. And the whole set up cost less than $20 bucks.
There are plenty of building material liquidation and resale shops around these days. If I were to find one of those tall faucets "goose neck" that was used for cheap, I could cut it about three inches back from the end the charcoal filter would install and fit this into the end of the adapter hose and secure it with aircraft clamps.
The other end of the hose that fits into the output side of the 0.5 micron filter could be purchased new
and secured to that end with an aircraft clamp as well. (this would be a cheap and dirty solution but would
no doubt be cheaper than going to a specialty hose shop and paying to have it made).
Again, I'm not filling big tanks but this would serve my needs for small scale needs where I'm not staying for extended periods.