I wouldn't.

Drinking water from the tanks of a boat that you own and use exclusively is one thing. You know how those tanks have been cleaned and maintained. On a charter boat, though, you have no clue.

We always get some pint-sized bottles, and some gallon jugs. Then we refill the bottles from the jugs, and refill the jugs at Trellis, Jost, or elsewhere that we can.