We go with one gallon per person for every 2 days of the charter. 1/2 gallon minimum per person per day. It’s a lot of gallon jugs but you’ll find creative places to tuck them on the boat :-) Gallon jugs - just let everyone refill their cups throughout the day (and here’s my pitch for everyone bringing their own tervis tumbler for the week!)

Don’t drink from the tank. We have a boat that we’re on all summer. We have 2 100 gallon water tanks. Think about this: the water comes through a hose, into a plastic tank, sits there, then gets refilled - all,charter season long. We use a brita water pitcher on our boat (not feasible for a charter I know).