Re: Drinking water tank water.
If you are afraid of your water system - don't use it for drinking water. If you know your system and maintain it and put "good" water in it then you should have no fear of it.
Bubblehead has it right. His practices will assure your potable water stays potable during routine operations if the water is not allowed to stagnate. Submarine sailors average use is about 19 gals a day per person (cooking/cleaning/showering/drinking/coffee) so the tanks have a frequent turnover of contents and good flow in the piping systems.
If you don't use your boat often and have stagnant water in your tanks and lines for long periods then you probably ought to haul water from Wally World for drinking.