Mold in RO System? Here Is What to Do!

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Dealing with mold is never pleasant, no matter where in your home it occurs.

Encountering mold in your reverse osmosis system can be especially problematic due to the health implications, though.

Here’s what you need to know about dealing with that situation and preventing it from reoccurring.

Key Takeaways

To clean your reverse osmosis system from mold, follow these steps:

  1. Shut off the water.
  2. Depressurize.
  3. Remove each filter element. Check to see if they have been affected by the mold. If so, throw them out.
  4. Clean each filter’s housing. Use bleach, white vinegar, or baking soda.
  5. Then, fill bleach into the first filter housing.
  6. Ensure there are no filters inserted into their housings before you turn on the water supply.
  7. Open the reverse osmosis faucet until water comes out.
  8. Allow the storage tank to fill.
  9. Wait for a couple of hours.
  10. Drain the tank.
  11. Refill and drain until you can no longer smell bleach.

How Does Mold Get into an RO System?

How does mold make its way into your reverse osmosis system in the first place? The reality is that it doesn’t take a lot for mold to start growing – all it needs is darkness, plenty of moisture, and a food source like minerals. The plumbing of the average house is the perfect environment for all these factors, as it tends to have lots of minerals built up along the interior walls from years of use.

Once mold starts growing in one part of your plumbing, it will eventually spread – and it will end up in your reverse osmosis system sooner or later. This is especially true for cases where the reverse osmosis system and its filters have been poorly maintained.

Under Sink Reverse Osmosis System

How to Remove Mold from RO Systems

In order to remove mold from your reverse osmosis system, you need to sanitize it. Here is a brief overview of the steps you need to follow, but make sure to check your manufacturer’s guidelines, because there will likely be some differences at various points:

  1. Shut off your water supply.
  2. Depressurize your reverse osmosis system.
  3. Take out every filter from its housing.
  4. Clean each filter’s housing. You can either use bleach, white vinegar, or baking soda.
    1. Bleach is the best option, as long as you make sure it’s regular, unscented household bleach. Dilute a couple of teaspoons in a large container of water and use that as your cleaning solution. Make sure to rinse properly after cleaning.
    2. You can also soak the entire housing in white vinegar, or spray it on using a spray bottle if it’s too large. Leave it covered in the solution for about half an hour, then rinse it thoroughly.
    3. Mix a little baking soda – ¼ of a tablespoon should do – with water and spray the mixture onto all areas affected by mold. Leave it for about 10 minutes, then scrub and rinse.
  5. Inspect each filter cartridge. Those that have been affected by mold will have to be thrown out and replaced – they can’t be saved.
  6. Inspect the water tank. If you suspect mold, you’ll have to sanitize it as well (later in the process).
  7. Finally, check all the tubing connections and valves, and clean them if necessary.
  8. Next, fill the stage 1 filter sump with about 3 tablespoons of bleach.
  9. Ensure there are no filters inserted into their housings, and turn on the water supply.
  10. Open the reverse osmosis faucet until you see water coming out, then close it.
  11. Check for leaks.
  12. Fill your storage tank completely. Leave it full for a couple of hours.
  13. Flush the whole system.
  14. Refill the tank and drain it. Repeat this process until you can no longer smell bleach.

How Can You Prevent Mold from Growing in Your Reverse Osmosis System?

Regular cleaning is the best way to ensure that mold never gets a chance to develop in your reverse osmosis system. You can also invest in a filter that specifically targets mold. UV filtration is probably the best option for that. However, this can make your setup more complicated, and the anti-mold filter may need some additional support as well. For example, UV filters require sediment pre-filtration for optimal performance, so you have to be careful about how you’re arranging the entire filtration setup.

Make sure your plumbing is well maintained, too. Fix any leaks as soon as you discover them – not just in the reverse osmosis system, but along your whole plumbing in general. Avoid keeping any porous materials close to areas prone to leaks, as those make the perfect home for potential mold growth.

Recurring Mold Problems

Mold is usually a symptom of a bigger underlying issue. Once it shows up, there’s a good chance it will come back after you’ve cleaned it. As long as the main cause is not addressed, you will still have recurring mold issues. That’s not always possible though, especially when it’s something rooted deep within your plumbing. In that case, you will either have to be more aggressive with your maintenance and cleaning, or invest in some specialized filters that can target mold.

macro shot of fuzzy mold


Regularly sanitizing everything with chlorine is one way to keep mold out. This is something you should do every once in a while anyway, but when you’re dealing with more aggressive mold attacks, you may have to increase the frequency. To chlorinate your RO system, you can follow the guide we provided above about sanitizing.

UV Light Filter

A UV light filter is perfect for killing mold and many other kinds of biological contaminants. It works based on the principle that many microorganisms die immediately upon being exposed to ultraviolet light.

These filters are very simple in their operation – it’s typically just an elongated UV light bulb situated in the middle of the filter’s housing, through which water runs. As water gets exposed to UV light, any mold in it will die. However, for this to work properly, water must be filtered with a sediment filter beforehand. Otherwise, floating particles can create shaded spots for mold to hide behind.

What Is Mold and What Are Its Health Effects?

Mold is a type of fungus. It thrives in dark, moist locations, and can often be found growing in porous materials, on dead plants and animals, and various kinds of decaying substances in general. Mold is all around us in nature – but it should still be avoided as it can cause various health complications in humans. Some of the symptoms of mold exposure include:

Allergenic Mold

Some types of mold are only problematic to people who have an allergy to them. These include Cladosporium and Penicillium. Normally, you won’t feel any ill effects from being in close proximity to these types of molds if you’re not allergic. But if you are, even small amounts can cause a severe respiratory response that might require immediate medical attention.

Pathogenic Mold

Pathogenic molds are much more dangerous, as they carry various pathogens that can affect the health of anyone, even someone who’s otherwise perfectly healthy. Some of the pathogens carried by these molds include A flavus, A terreus, and A fumigatus. Pathogenic mold growths can be removed with the use of disinfectant, but you must always consult an expert when you realize the growth is larger than you initially thought.

Toxic Mold

Toxic molds are the most dangerous of the three categories, as they can be extremely harmful to humans and many animals. It’s important to understand that becoming affected by a toxic mold growth doesn’t require direct contact or ingestion. It’s sometimes enough to just inhale the spores that are freely floating in the air around you. If you’re not aware of the presence of mold in the area, you might be unwittingly exposing yourself to it on a regular basis, with the associated health issues accumulating and progressively getting worse.

If you have any questions about mold in RO systems 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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