Bacteria can accumulate in the fresh water tank and water lines, especially if that water supply has not been used frequently and has not been replenished with fresh, clean water on a regular basis. When you take your RV out of storage or it has been used exclusively on a city-water connection, the tank and entire water system should be sanitized before use.
Add 1/4 cup of household bleach for every 15 gallons of tank capacity. Top off the water tank with fresh water. This will mix the contents. You can also mix the solution by driving the RV around the block.
Pump water through each faucet so that all the lines are filled with the water/bleach solution; You can smell the bleach when it reaches the faucet. Don’t forget the shower and any external faucets/showers.
Run sufficient water through the hot-water faucets to completely purge and replace the old water with the bleach/water mix from the fresh water tank. Alternatively, the hot water tank can be drained via its drain valve, and refilled with the bleach/water mix by the water pump.
Let the water in the tank and lines sit for several hours. Then drain the entire water system, including the hot-water tank. Fill with fresh water, and run it through the system to flush the lines
If a bleach odor remains, mix 1/2 cup of baking soda with a gallon of water and pour into the freshwater tank. Some folks add vinegar instead of baking soda.
If your RV does not have a gravity feed fresh water fill tube, you can introduce the bleach by pouring it into an empty water hose hooked to the the city water inlet and turn on the water spigot