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Sanitizing Your Freshwater Holding Tanks & Removing Algae

  • 4 min read


  1. It's very important to sanitize your RV freshwater tank at least once a year to prevent contaminants or algae build-up. These contaminants and algae can be very harmful to your health!
  2. Because we are dealing with the RV freshwater tank and not the black or gray tanks, it's not as important to avoid using anti-bacterial products. In fact, bleach and anti-bacterial products are pretty much your only option for sanitizing your tanks.
  3. Follow the step-by-step guide below to sanitize your RV freshwater holding tank using either bleach or an anti-bacterial product. 
  4. Often, people will complain that the water from their freshwater tank tastes gross. There are ways to freshen the water. We will be covering this topic in a future article, so check back!

If you’ve been RVing for any length of time, it’s likely that you’ve heard a whole lot about RV holding tank maintenance. In fact, we have written many articles about how to properly care for your holding tanks using The Unique Method! But there’s a topic that often gets pushed to the side when it comes to properly maintaining your tanks: how do you deal with dirty, contaminated fresh water and algae build-up in your freshwater holding tank? 

In all honesty, algae build-up is relatively unlikely, because algae needs some form of sunlight in order to grow. However, this is possible if, for example, your RV has clear water lines. It is very important that you sanitize your tanks regularly, because this is your drinking water, and no one wants tainted drinking water! It's also important to prevent algae blooms in your freshwater tank as it can be harmful to your health! In this guide, we’ll provide you with a step-by-step guide to sanitize your RV freshwater tank using bleach and/or an antibacterial product!

Using Bleach or Antibacterial Products

Okay, we know what you’re thinking: how can they recommend bleach and antibacterial products when every other guide on their website says not to!? This is a fair question. 

There are two things to consider here: 

  • We are dealing with the RV freshwater tank, not the black or gray tanks, which means that the rules are completely different. In your black and gray tanks you WANT a thriving culture of bacteria (aided by a high-quality, bacteria-based holding tank treatment) to assist in waste breakdown and odor elimination. In your freshwater tank you DO NOT WANT any bacteria as this is the source of your drinking, hand-washing, and bathing water.
  • If you want to thoroughly sanitize your freshwater tank, ultimately the only way to do this is by using bleach or antibacterial products. These sorts of products are pretty much the only option to sanitize the freshwater tank in your RV, but don’t worry; you’re going to make sure the tank is completely clean before you use it again!

A Step-by-Step Guide

To sanitize your RV freshwater tank with either bleach or another anti-bacterial product, follow these checklist steps:

  1. Turn off your hot water heater and wait a few minutes before proceeding to the next step. 
  2. Locate the outside compartment where your water heater is placed and open the pressure relief valve. 
  3. Empty your water lines. Since algae and contaminants can build-up in the water lines of your RV, you’ll need to start by making sure they’re empty. You can do this by locating and opening your low-point water drainage valves. You may also need to open the drain on the freshwater tank itself. Your RV owner’s manual should tell you where these valves are located.
  4. Once your water lines and tank are totally empty, it’s time to mix your bleach solution. For every 15 gallons that your RV freshwater tank holds, you should mix about 1/4 cup of bleach with a few gallons of water in a bucket. 
  5. If you choose to use an antibacterial product to sanitize your tank, follow the product directions to determine how to mix your solution. 
  6. Carefully pour your solution into your freshwater tank. Using a funnel might make this a whole lot easier and lower the potential for staining of the area. 
  7. After you’ve poured your bleach/antibacterial solution into the tank, fill the tank with freshwater until it is almost full. 
  8. Run water through all of the sink faucets, one at a time, to fill the lines completely. Do not run the faucets so long that you empty your freshwater tank! You should smell bleach coming from each faucet. 
  9. Some RVers find it helpful to take a short drive once every water line is filled with the bleach/antibacterial solution. This drive can help to slosh the water around and further sanitize the system.
  10. Let the solution sit in your water lines and freshwater tank overnight. 
  11. After you’ve let the solution sit overnight, drain the freshwater tank and water lines into a proper waste receptacle. 
  12. Completely fill your tank with freshwater and turn on your faucets, one at a time, to completely flush your lines so only fresh water remains in the lines. You should repeat this step until there is no longer any bleach smell in the tanks or from any faucets.


To help prevent contaminants and algae from building up in the first place, you should go through this sanitization process with your tanks every six months to once a year. Because algae is relatively unlikely in freshwater tanks, it should be fairly easy to prevent if you regularly sanitize. Simply complete the steps given above, and you should have an algae-free RV freshwater tank! We would love to answer any questions, concerns, or comments you might have about this topic! Please reach out to us for help. Happy Camping!

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