You can use Mylar Foil bags as liners in your buckets. Here is an example. I'd go with the heat seal bags rather than the ziplock bags. I've never ordered from the company I linked to, it's just one that I've been looking at for potential supplies.

Also, though you can buy a heat sealer, it's possible to heat seal Mylar Bags with a regular clothing iron.

After that, I sort of got lost in what you were asking regarding your water supply.