Algae in RO System? Here Is What to Do!

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Noticing algae growth in your reverse osmosis system can happen more often than you might assume.

It’s generally not a cause for concern, but it should still be dealt with promptly, as it can cause various health complications.

Here’s what you need to know about algae growing in your reverse osmosis system, how to deal with the problem, and how to stop it from reoccurring.

Key Takeaways

Here is what to do if you have algae growing in your RO system:

  • Sanitize the system on a regular basis.
  • If the algae keeps reoccurring, consider adding UV treatment to your setup. A chemical injection system can help, too.

Why Is There Algae in My RO System?

Algae can make its way into your reverse osmosis system either from your water source, or even directly from within the system itself. Algae isn’t very pretentious about the conditions it grows in, so it only takes a little for a full-blown growth to develop in a compromised part of your system.

Algae in the Source Water

Sourcing your water from a well is a very common cause of algae contamination. In fact, it’s something you will need to specifically address if you’re obtaining your water from a well in almost every case. After all, a well is the perfect environment for algae to grow in. Well water is full of contaminants that are useful to algae as nutrients, and it tends to have high pH levels and relatively little movement. All of those factors predispose to algae growth.

algae with bubbles in water

Algae Growing in the Reverse Osmosis Water Filter Itself

It’s also possible that the algae are coming from within the reverse osmosis system itself. As long as there’s a spot that offers the ideal conditions, all you need is a small initial growth.

There’s also the problem that reverse osmosis filtration may be a little too thorough for its own good in this case. Specifically, reverse osmosis systems remove chlorine and chloramine from water, which normally kills algae. This means that the later filter stages as well as the storage tank of your reverse osmosis system will likely be an ideal environment for algae growth.

How to Get Rid of Algae in a Reverse Osmosis System? Sanitize!

The only way to get rid of algae in your reverse osmosis system is to thoroughly sanitize it. To do this, follow these steps – but also consult your system’s instruction manual, because there will likely be some steps that are unique to your own model and setup.

  1. Shut off the water supply.
  2. Drain and depressurize the reverse osmosis system completely.
  3. Remove all filters from their housing.
  4. Sanitize each housing unit separately. Use a bleach solution for the best results. Mix ¼-½ a tablespoon of bleach into a bucket of water, and scrub each housing with that solution thoroughly. Afterwards, rinse each housing and let it air dry.
  5. Sanitize the interior of your storage tank as well. Before doing that, disconnect it from the rest of the system, and add a little bleach to the input tubing. After that, reconnect the tank to the reverse osmosis system. Turn the water back on.
  6. Open the RO faucet till water comes out. Let the tank fill up completely. Let it sit like that for 1-2 hours to ensure thorough sanitization.
  7. Open the reverse osmosis faucet again and allow the tank to drain completely. Repeat this once more to ensure the system has been properly flushed.
  8. Turn off the water supply.
  9. Reinsert all filters back into their housings.
  10. Turn on the water supply.
  11. Check for leaks.

If you’re obtaining your water from a well, you must sanitize the well separately. Shock chlorination is the most popular method for accomplishing that.

  1. Add plain bleach in diluted form to your well. How much exactly you’ll need will depend on the well’s diameter and depth. Follow the CDC guidelines for using chlorine on well water.
  2. Use a hose – preferably a brand new one – to pour water into the well, allowing it to circulate.
  3. Rinse the well walls as much as you can until there’s no chlorine left.
  4. Turn on all faucets in your home and wait until you notice the smell of chlorine. Make sure to turn on hot faucets as well if you have a water heater.
  5. Wait a while, then turn off all faucets and wait for up to 12 hours to let the chlorine do its work.
  6. Open a faucet and keep it running until you can’t smell chlorine any longer. Do the same for each faucet and water fixture in your home.

How to Prevent Future Algae Growth

Preventing algae growth is all about minimizing the factors that lead to it in the first place. This means that you should limit exposure to sunlight, and avoid having your water sit still for too long. Ideally, your entire filtration setup should be kept in a dark, cool place. That’s why many people use their basement for a whole house filtration setup.

You also need to keep your system clean and sanitized on a regular basis. If you don’t have particularly aggressive algae growths troubling you, it’s enough to do that every 6-12 months to stay on the safe side. And of course, make sure to replace each filter according to its prescribed schedule. Different filter elements have different requirements in this regard, so check the manual for more information.

Different Water Filter Cartridges and Membranes

If algae are still proving problematic, you may also want to revise your approach to water treatment slightly. Specifically, look into adding a UV filter or a chemical injection system to your setup. This will kill any algae and most other types of biological contaminants with a close to 100% efficiency.

Is Algae in Drinking Water Harmful to Your Health?

This depends on the type of algae. Green algae are generally harmless, although it should still not be ignored.

Some specific types of algae can be very harmful to humans though, causing irritation, allergic reactions, and even producing toxic substances in some cases. These toxins are sometimes so strong that they affect not just the water they reside in, but everything else in that water as well. For example, you could get poisoned by eating seafood from a water reservoir with toxic algae growth.

Another Reason Why Reverse Osmosis Water Can Be Green: Corroding Copper

Any signs of coloration in your water should be investigated in more detail. When it comes to green water in particular, many people’s immediate reaction is to assume it’s algae by default. But you should remember that green water can also be caused by another factor: corroding copper from your plumbing and making its way into your water.

This is especially problematic when you’re using a whole house reverse osmosis system, because reverse osmosis water is often slightly acidic and highly pure, and therefore more prone to corroding copper. What to do? Get the proper post-treatment in place. For example, a calcite filter will help you balance water pH levels and add some minerals back into the water.

If you have any questions about algae in reverse osmosis 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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