Bacteria in Reverse Osmosis Tank – What You Can Do About It

This page may contain affiliate links. If you buy a product or service through such a link we earn a commission at no extra cost to you. Learn more.

Bacteria in your reverse osmosis tank can be a serious issue that demands immediate attention. Several causes could be leading to bacterial contamination, so you’ll want to diagnose the source of the problem before you can solve the issue.

RO storage tanks can act like magnets for bacterial growth, which is why regular cleaning and sanitizing of the entire system including the tank is so important. The last thing you want after investing all that money in an advanced water filtration system is for it to turn into a petri dish!

Let’s take a look at the possible causes for bacterial growth in your RO tank – and what you can do to fix them.

Key Takeaways

  • Bacteria in your reverse osmosis tank is a major issue that should be addressed right away to avoid potential health effects. The first thing to do is cease drinking water from the tank. Next, you’ll want to sanitize the tank using household bleach and flush it out thoroughly.
  • While sanitizing your tank will eliminate the bacteria inside, it won’t eliminate the source of the contamination. Bacteria in a reverse osmosis tank can be perfectly normal, provided said tank hasn’t been sanitized for a while, but if you suspect your feed water to be the problem, you might need to further investigate.
  • If your water is supplied by a well, you may need ‘shock chlorinate’ it. If you are on municipal water, reach out to your water utility and let them know about the problem.
  • Another option when you’re dealing with bacterial contamination is adding a UV filter stage to your existing RO system.

What to Do If You Have Bacteria in Your Reverse Osmosis Tank

The first thing you want to do if you find bacteria in your reverse osmosis tank or system is stop drinking the water immediately.

With that said, reverse osmosis tanks act like magnets for biofilm and bacterial contamination. So if you haven’t been keeping up with the scheduled maintenance, bacteria accumulating inside your RO tank is perfectly normal. Good news is, you already know what the problem is. You’ll need to clean and sanitize the entire system using unscented bleach (more on that below) and discard and replace all filter elements.

If you suspect your well water supply to be the problem, then you have to eliminate the contamination at the source. You can use the ‘shock chlorinate’ method to kill off any microbiological contamination. This involves pouring a set amount of chlorine down your well and then thoroughly flushing every faucet in your house until you no longer detect any chlorine smell.

If your water supply is municipal water, then shock chlorination will not work. In this case, contact your water utility and let them know about the problem. There might be a leak in the service line leading to your home that needs fixing. In the meantime, consider adding a UV filter stage to your RO system.

A UV filter is the ideal filtration method for removing bacterial contaminants from your drinking water. It’s not so much a “filter” as a bacterial eradicator, as it doesn’t remove anything from water. Rather, it kills over 99.99% of microbial contaminants.

plumber installing reverse osmosis system under sink

Where Does the Bacteria Come from?

Bacteria generally enter a reverse osmosis system from your feed water. Again, this is perfectly normal most of the time. Only if you suspect a problem with your source water should you further investigate.

Because reverse osmosis membranes are ultrafine filters they will filter anything larger than .0001 microns. Even the smallest bacteria are 0.2 microns in size, so the RO membrane will block any bacteria and trap them in the membrane.

This is a positive in that it won’t let bacteria past the membrane and into your drinking water, but it can also lead to bacterial overgrowth inside the membrane and membrane housing. Eventually, this will affect your RO tank, too.

How to Sanitize an RO Water Tank That Has Bacteria Inside

The basic premise of cleaning and sanitizing an RO tank (and system) is adding a small amount of chemical disinfectant to the tank and system, wait, and then flushing it out until no chemical smell remains.

While you can sanitize a reverse osmosis tank on its own, if you suspect bacterial growth then you’ll generally want to sanitize the entire filter system at once. This will involve removing and replacing the filter elements and membrane as well as flushing the filter housings.

As for your tank, all you need to complete the cleaning process is unscented household bleach (or hydrogen peroxide, chlorine, or a dedicated tank cleaner) and a funnel or eyedropper.

Here’s how to sanitize an RO tank:

  1. Turn off the feed water valve to the RO system.
  2. Open the RO faucet and allow any remaining water in the system to drain.
  3. Close the RO faucet after the water has drained.
  4. Close the valve on top of the storage tank and disconnect the tubing from the rest of the system.
  5. Use the funnel or eyedropper to add ½ a teaspoon of bleach (or another cleaner) to the tank tubing.
  6. Reconnect the tubing to the rest of the RO system and open the tank valve.
  7. Turn on the feed water supply valve and allow the storage tank to fill. This can take between 2 and 4+ hours.
  8. When the tank is full, let the cleaning solution soak for between 30 mins and 2 hours.
  9. At this point, open the RO faucet and allow the storage tank to drain. Then repeat the filling and draining process a second time. There should be no chemical smell coming out of the faucet, but if there is refill the tank and discard it once again.

If you have a post-filter it will need to be discarded after this process unless you bypass it to avoid the cleaning solution.

The process is similar if you want to sanitize the entire system, but instead of adding the cleaning chemical to the tank, you’ll remove the filters and membranes from their housings and add the chemical to the first pre-filter housing. Then let it flush through the entire unit.

How to Stop Bacteria from Growing in Your RO Tank Going Forward

The best way to avoid this problem from happening in the first place is to perform the scheduled cleaning and sanitizing process. Generally, this should be done every 6 to 12 months, but consult your system’s manual for precise recommendations.

Does Reverse Osmosis Remove Bacteria? How?

Reverse osmosis membranes will remove most bacteria and viruses from water, but they aren’t designed for this purpose. While they will prevent most bacteria from getting past the membrane stage, they don’t eliminate microbes, hence they can allow bacteria to thrive in the membrane and pre-filters deteriorating them. This is why most reverse osmosis systems state they are designed to be used with “biologically-safe water”.

If you suspect you have an issue with bacterial contamination you should try to eliminate it at the source. The next best option is to add a UV water filter to your RO system setup.

How to Kill Bacteria with Your RO System

Adding a UV filter stage to your RO system will give you the best of both worlds when it comes to water purification. It will remove a wide range of organic and inorganic contaminants via the membrane and filters as well as kill off any microbial contamination by the UV light.

bacteria in water

Health Effects of Bacteria in Drinking Water

When it comes to bacteria in drinking water, it’s not always an indication that the water is unsafe to drink.

Some bacteria, known as total coliform bacteria are relatively harmless, whereas other microbes like E. Coli, campylobacter, legionella, and salmonella can lead to a wide variety of symptoms. Common are diarrhea, vomiting, stomach cramps, upset stomach, and fever.

Suffice it to say that the presence of bacteria and other pathogens in your drinking water is something that should be avoided. Most municipal water sources in the US are very good at eliminating microbial contamination, but if your water is supplied by a well you’ll have more cause for concern.

If you have any questions about bacteria in your reverse osmosis tank please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
Learn more about .

Gene

Information provided on BOS is for educational purposes only. The products and services we review may not be right for your individual circumstances.
We adhere to strict editorial guidelines. Rest assured, the opinions expressed have not been provided, reviewed, or otherwise endorsed by our partners – they are unbiased, independent, and the author’s alone. Our licensed experts fact-check all content for accuracy. It is accurate as of the date posted and to the best of our knowledge.

Leave a Comment: