Sorry, forgot to mention - we were only two on board. We planned that you should have 1/2 - 3/4 gallon per person per day to drink for your worst-case scenario time at sea. For us we said this was 50 days, giving 75 gallons.
I average about 1 gal/day in moderate temps and clean raw water available,
that includes showers. I have a raw water spigot in the galley, so I can use
raw water to soak dishes and visually clean them, then use fresh to actually
wash/rinse the mostly clean dishes, using very little water.
Also can dive in to bath and just rinse with fresh water.
So unless you don't plan on showering and are going to eat nothing
but pop-tarts, I would plan on a higher water usage rate.