I have a 1976 Oday. The water tank is a 12 gallon 1976 water tank. I am the third owner. A basic water and Clorox rinse 9 years ago when I bought the boat made me feel more confident but I decided to use the tank water for dishwashing and hand washing etc,etc. I have a two gallon Rubbermaid jug for drinking water and some extra 1 gal. cider jugs. On a recent twelve day trip to Lake Champlain the jugs supplied all the drinking water and the 12 gallon tank took care of chores, with three refills from the lake and from marina hoses for the 12 gallon tank. BTW, I have an electric pump
-faucet and that movers a lot of water at a time so I was rather profligate with my fresh water supply. But drinking water came from known, pure supplies kept in portable bottles.