Potable water storage tanks, such as those used in RVs, should be sanitized after long periods of storage, as well as when water of questionable quality has been added to the tank. Sanitizing is a process designed to kill all organisms that might be in the water. Although there are commercial solutions for the purpose, many people use and swear by regular household bleach.
The Sanitizing Process
To sanitize the freshwater tanks in your RV, distribute a sanitizing solution through the water system. Add one-fourth a cup of household bleach per 15 gallons of water to make a concentration of chlorine strong enough to kill any harmful bacteria. Mix the bleach in 1 gallon of water before adding to the empty tank. Fill the tank to 1/2 full after adding the bleach solution. The process of adding water to the tank will further ensure the complete mixing of the bleach in the half full tank. Open all faucets and run the RV water pump until the smell of bleach is noted at each. Then close the faucets and take the RV for a ride. This will splash the solution, wetting the entire surface of the tank. After you return to your home base, allow the bleach solution to remain in the tanks for a minimum of 12 hours. Drain and repeatedly rinse the tank and plumbing to as much of the bleach smell as possible.
Removing the Chlorine Smell
As effective as bleach is as a sanitizer, it does have one drawback: It leaves a residual chlorine smell in the tank. Some RVers suggest adding baking soda to the tank to remove the smell. Others suggest that distilled vinegar does a much better job and has the added benefit of removing mineral deposits. If using this method, add 1 quart of vinegar per 5 gallons of water. Allow the solution to sit in the tank and plumbing for at least 24 hours before draining, rinsing and refilling the tank with fresh water.