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How to Sanitize Your RV Fresh Water Tank

by Doug and Michelle
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Your RV fresh water tank is your clean water source for washing hands, doing dishes and maybe even cooking while on the road. It’s important to sanitize your RV fresh water tank regularly.

There are a lot of different recommendations out there on how to sanitize a water tank. We break down the most safe and effective way to sanitize, using water safety standards and chemical safety best practices.

Why Sanitize Your Fresh Water Tank?

We love water, and so do harmful organisms like yeasts, molds and bacteria. As water sits in your storage tanks, these organisms can grow and contaminate the water you use for washing or preparing food.

It’s important to have a sanitizing schedule for your RV fresh water tank to keep everyone on board happy and healthy.
In between sanitizing, we recommend draining and flushing your water system when not in use for long periods. This helps deprive bacteria, yeasts and molds of the moisture they need. (Keep in mind some organisms will survive even in a dry system.)

How Often Do You Need to Sanitize?

No matter how often you use your RV fresh water system, the best practice is to sanitize your fresh water tank at least twice a year.

Here are some other times when it might make sense to sanitize:

  • After taking your RV out of winter storage, or any other time it has sat idle for long periods
  • Before you winterize your RV for storage
  • Before using a rental or borrowed RV
  • After using a water source, you learn may have been contaminated
  • After noticing any bad odor, discoloration or sediment in the water coming from your faucets

Step by Step Procedure

Materials Needed

  •  Household bleach (5% chlorine)
  • Water hose connected to clean water source
  • Large pitcher or jug
  • Large funnel
  • Chlorine test strips (optional)

Prepare RV Water System

Note: Refer to your RV manual for specific instructions on the following.

  1. First you will need to prepare the water system to avoid damaging sensitive parts such as your water heater and water filter.
  2. Turn off the water pump.
  3. Turn off the ice maker if you have one.
  4. Next turn off and bypass your water heater. Your water heater will generally stay hot enough to kill any harmful mold and bacteria, and the chemicals used could damage components.
  5. If you have a water filter, either remove or bypass the filter.
  6. Drain your fresh water tank by opening the drain valve, and then close and tighten the valve again.

Make Up Chlorine Solution

  1. In order to get a safe and effective dosage of chlorine, you need to know how many gallons your fresh water tank holds. Check your owner’s manual to find out.
  2. Calculate the amount of bleach needed for your fresh water tank.

The Minnesota Department of Health recommends using a 50 ppm chlorine solution to sanitize water storage tanks.

Using common household bleach which contains 5% chlorine, you will need 1/4 cup (2 ounces) of bleach per 16 gallons in your fresh water tank.

For example, with a 40 gallon fresh water tank –

2oz / 16 gal = 0.125oz per gal X 40 gallons = 5 oz (2/3 cup) bleach

  1. Fill a large pitcher or jug about halfway with clean water, and then add the bleach to the water. Then fill the rest of the way with water to further dilute the solution.

Safety note: Adding the bleach to water instead of an empty container will reduce the risk of splashing concentrated bleach.

Add Chlorine to Fresh Water Tank

  1. Hook up a water hose to a clean water source and fill your fresh water tank about 1/4 full of water. Remove the water hose.
  2. Using a funnel, carefully add the chlorine solution to the fresh water tank. Again, it’s always best to add the chlorine solution to water instead of an empty tank, to avoid getting concentrated bleach somewhere you don’t want it.
  3. Now continue to fill your fresh water tank until you see overflow, confirming the tank is full.

Flush Water System with Chlorine Solution

Now that you have chlorinated your fresh water tank, you need to run the solution through all of the water lines and faucets to sanitize the entire water system.
  1. Turn your water pump back on.
  2. One at a time, run water through each of your faucets and your shower, including any exterior kitchens or showers.

Let each faucet run until you can smell bleach, then turn the faucet off and move on to the next faucet.

Be sure to run cold water and then hot water separately, to sanitize both the cold water and hot water lines. The hot water that comes out will be cold, since you have bypassed your hot water heater.

  1. Now top off your fresh water tank with clean water, to replace the water you flushed through the water lines.

Let the Chlorine Solution Set

  1. Sanitizers such as chlorine need a minimum contact time with surfaces in order to be effective. Allow the solution to sit in the water lines and tank for 24 hours.

If leaving the solution sit for 24 hours is not practical, the Minnesota Department of Public Health recommends you increase the chlorine concentration to 200 ppm and allow it to sit for 3 hours.

To get 200 ppm, multiply your previous calculation by 4. For our example 40 gallon fresh water tank, we now need 20 oz (2 1/2 cups) bleach.

Test Your Free Chlorine

  1. After the solution has sat for the recommended time, you may want to check your free chlorine levels to verify the sanitization was effective.

As chlorine sanitizes, it reacts with substances and bacteria in the water and gets consumed. Free chlorine is chlorine that has not been used and is still available to inactivate bacteria.

If you have no detectable free chlorine left, that means you ran out of chlorine and could have bacteria left in your water system.

The Center for Disease Control uses the presence of free chlorine as a measure of water potability, which means how safe it is for drinking.

The best practice is to repeat steps #11-19 until you have free chlorine left over at the end of the process.

You’ll want test strips that can detect free chlorine down to 0.5ppm. Test strips intended for pool water will only go down to 10 ppm. This won’t let you see low levels of free chlorine, which is all you need. You will need water quality test strips instead.

Water quality chlorine test strips may be found at local hardware stores, or check out these Hach Chlorine Strips. Make sure you look at ‘Free Chlorine,’ not ‘Total Chlorine.’

Drain and Rinse Water System

  1. Now it’s time to drain and rinse your water system. Open the gray water tank drain valve to allow the water to drain to the ground, or hook up to a dump station to drain the water as you rinse.
  2. Turn on each faucet in the RV and run water until the fresh water tank is empty.
  3. Refill your fresh water tank with clean water. Turn on each faucet in the RV again, and run clean water until you can no longer smell bleach at each faucet.

Safety note: If the bleach odor persists after the fresh water tank is empty, refill the tank and repeat the process until the bleach smell is gone.

  1. Refill the fresh water tank with clean water. Close and tighten the gray tank drain valve.
  2. You may want to use your free chlorine test strips to verify safe chlorine levels at this point.

Drinking water systems are treated with a target of 2ppm free chlorine, and should have no more than 4ppm free chlorine present. If you have free chlorine levels higher than 4ppm, you may want to repeat steps #18-21.

Turn Everything Back On

Note: Refer to your RV manual for specific instructions on the following.

Your fresh water system is now sanitized, and you’re ready to undo everything you did to prepare your RV water system.

  1. Turn the water heater back on (if needed) and turn off the water heater bypass.
  2. Install the water filter if you removed it, or turn off the bypass..
  3. Turn the ice maker back on, if you have one.

You are now ready to use your sanitized fresh water system.

Ahh, Clean Water!

We hope this was helpful in safely and effectively sanitizing your RV fresh water system. Comment below and let us know how this worked for you, and share your recommendations!

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