I have a 45 year old boat with the original integral tanks, and we drink the water with no problems. An occasional shot of regular unscented chlorine laundry bleach is all you need. Recommended dose is .13 ounce per gallon of tank capacity. Pour that amount into the empty tank, then fill with cool water. Run that through all the lines to the taps and let it sit for a couple hours, then drain and refill the tank. If your water is still funky, the problem is often in the hoses. If they're the clear vinyl kind and you see green algae inside the hose, you'll probably have to replace them to truly get rid of it. It's the light penetrating the hose that allows stuff to grow inside. I changed mine to opaque PEX tubing and haven't had any more problems. Filling the tank with treated municipal water usually keeps enough chlorine in the system to keep it fresh. If the hot water stinks but cold is ok, it's because heat evaporates the chlorine and lets stuff grow in the hot water lines. You don't get that problem in your home because the water there is always hot and won't let anything grow. If you use the hot water taps to get cold water when there is no hot, that will keep them flushed out and minimize the problem. If you're really paranoid, you could take a water sample to your local Health Department and have it tested. People with well water at home have to do that occasionally.