Written by: Gene Fitzgerald // Last Updated: Mar 14, 2023
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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
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.
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.
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:
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.
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.
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.
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.
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!
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