If it is dampish, for drinking water I generally just catch water off the tent fly or rain cover tarp (first choice) or spread a tarp in a dip and hope the little bastards don't think it is a custom built swiming pool for them for the few days I'll be using it. Hot drink and food water gets boiled anyway.
A carry along filtration system for away from camp/run out of canteen water scenario.
Rinse a new water tarp well first, or the water tastes funny from, I assume, manufacturing residue which probably isn't that good for you......
