The generally accepted method of sanitizing your RV's fresh water system as outlined below involves filling the fresh water tank with a solution of household bleach and running the solution through each faucet. Then letting it stand for at least three hours. Finally, flush the system once or twice to remove the taste and smell.
This procedure is one you'll find in most any book about RVing is tried and true but be sure to read on to find out what I do.
Start with a nearly full fresh water tank.
Turn the water heater off and let the water cool.
Dilute 1/4 cup of household bleach into a gallon of water for each 15 gallons of tank capacity.
Add the chlorine/water solution to the water tank. Never pour straight bleach into the RV fresh water tank.
Turn on one faucet at a time and let the chlorinated water run for one or two minutes. You should be able to smell the chlorine. Make sure you are using the water pump and not an external water supply.
Top off the RV fresh water tank and let stand for at least three hours over night is better.
Completely drain the system by flushing the faucets for several minutes each. Open the fresh water tank drain valve to speed up emptying the tank. Then open the hot water tank drain plug and drain until it is empty.
Close all valves and faucets and drain plugs.
Refill water tank with fresh water, then flush each faucet for several minutes until the tank is again empty. Make sure you are using the water pump and not an external water supply.
Fill the tank again. The water should now be safe to drink but if the chlorine odor is too strong you can repeat the fresh water flush.
Your RV fresh water system should now be safe for use.