Can Bacteria Grow in RO Water?

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Reverse osmosis water is highly pure.

Does that mean without any organic and inorganic impurities, bacteria won’t be able to grow in RO water?

Let’s find out!

Key Takeaways

  • Yes, it is possible for bacteria to grow in reverse osmosis water, given the right circumstances.

Can Bacteria Grow in RO Water?

So, can bacteria grow in RO water?

Yes, bacteria can grow in reverse osmosis water under certain conditions. While RO systems are highly effective at removing bacteria, if the water stays undrained in the pipeline or tank for an extended period, bacterial formation can occur.

In terms of growth rates, bacteria forming biofilms have been found to grow at a significantly slower pace in RO water. The total specific cell growth rate is equivalent to a doubling time of approximately 9.1 to 10.1 days.

This means that post-disinfection measures must be considered when designing and operating an RO system to mitigate the risk of bacterial growth in the permeate water and throughout the RO system itself.

bacteria in water

Can Bacteria Grow in a Reverse Osmosis System?

Yes, it is possible for bacteria to grow in a reverse osmosis system. One study aimed to understand how effective reverse osmosis is in treating drinking water to ensure it remains biologically stable within the RO system, free of harmful bacteria.

In this study, two types of RO membranes were used. The researchers created experiments to see how much bacteria would grow in the water after it had been treated with RO and then flowed through a model of a water distribution system. They didn’t use any disinfectants in this experiment.

The results showed that the RO membranes did an excellent job of improving the water quality. They removed most organic matter (including bacteria) and over 99% of bacterial cells, leaving less than 50 cells per milliliter of water.

However, despite the low level of nutrients and bacteria in the treated water, the researchers found that significant amounts of biofilm (a group of microorganisms where cells stick to each other on a surface) accumulated in the model distribution systems. This means that even though the water was initially purified, bacteria could still grow.

The researchers calculated that the bacteria could double every 9.1-10.1 days under these conditions. This suggests that while RO treatment is effective at initially purifying the water, it doesn’t prevent future bacterial growth.

Therefore, RO-treated water isn’t biologically stable in the long term. To ensure the water remains safe to drink, further steps, such as post-disinfection, may need to be taken to minimize bacterial growth after the RO process.

Bacteria in the RO Storage Tank

Bacteria in the RO storage tank can pose a genuine concern. The issue arises from the fact that RO systems eliminate chlorine from tap water, leaving no bacteriostatic or bacteriocidal agent to combat contamination that may occur after the purification process.

This is why it is key to not let your purified RO water sit in the tank for too long (more than a few days).

What to Do If You Have Bacteria in Your RO Water/System

If bacteria are detected in your reverse osmosis tank or system, cease consumption of the water right away. If proper maintenance has not been consistently performed, the accumulation of bacteria inside your RO tank is to be expected. The positive aspect is that you have already identified the issue. To resolve it, you must thoroughly clean and sanitize the entire system using unscented bleach and replace all filter elements.

Where Does the Bacteria Come from?

Bacteria typically enter a reverse osmosis system through the feed water. Due to their ultrafine filtration, reverse osmosis membranes can effectively block substances larger than 0.0001 microns, including even the tiniest bacteria measuring 0.2 microns. This prevents bacteria from passing through the membrane and contaminating your drinking water. However, it can also result in the accumulation of bacteria within the membrane and its housing, eventually affecting the functionality of your RO tank.

How to Prevent Bacterial Growth Going Forward

To prevent this issue from occurring in the first place, it is crucial to carry out the scheduled cleaning and sanitizing procedure. It is advisable to perform this task every 6 to 12 months; however, for accurate guidelines, refer to the manual of your specific RO system.

under sink reverse osmosis system

Health Effects of Bacteria in RO Water

Bacteria and other harmful pathogens in water can lead to various health issues. These can range from gastrointestinal problems such as diarrhea, vomiting, and cramps to general discomforts like nausea and headaches. More severe symptoms can include fever and fatigue.

While these symptoms are unpleasant, they typically do not seriously threaten individuals with a healthy immune response. On the other hand, people with compromised immune systems need to be cautious, as these complications could potentially become life-threatening.

If you have any thoughts about the question, can bacteria grow in reverse osmosis water, 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.
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