Reverse Osmosis and Coffee

in Brewing Coffee

Question: “How will using reverse osmosis water in my coffee maker affect the flavor? Is it a bad choice?” – Tina

Answer: I’m hearing more and more about water filtration and purification systems in the home, and reverse osmosis continues to come up.  I’m by no stretch a chemist, but I’ve made a valiant attempt to understand how RO works and will do my best to explain it, leading to how that would affect the taste of your coffee.

RO works by creating two “chambers” separated by a membrane.  The membrane acts as a filter that removes unwanted chemicals and particles from the water in the first chamber, which (along with some waste water) is flushed into sewage, while the second chamber contains a purified water that pours from your tap for cooking and drinking.

So, the short answer to your question is that not only will it not affect the flavor of your coffee adversely, but it will likely make it taste even better.  Water is one of the most underrated ingredients in making good coffee at home.  Fresh roasted whole bean coffee and unfiltered water still make only a mediocre coffee.  When I use my drip brewer, I only pour filtered water from the Brita in my fridge, or I use one of two methods that involve boiling water – the French Press or the pourover method.  So, I did further research comparing RO to boiling water as purification methods.

While RO is certainly more convenient than having to boil water each time you want to use it, it ALSO appears to be a better system for purifying water.  The membrane in RO will stop many unwanted particles from ending up in the water that you drink.  While boiling water will kill bacteria, it will only move unwanted particles around in the water which will end up in your cup.

So enjoy your new RO system!  I think you will find that it has a very favorable effect on your coffee.  Thank you for the question.


  1. We use a RO at home and we use it for our coffee… love it.

    Comment by Robin — November 19, 2011 @ 10:58 am

  2. Very interesting, Robin. It would be neat as an experiment to see if there is a noticeable difference. I hope I did the definition of RO justice :).

    Comment by Marc Wortman — November 19, 2011 @ 3:54 pm

  3. Try using a blended RO water to bring out some of the subtle tastes of coffee, rather than pure RO which tends to overextract the beans and can surpress the more subtler flavours. Try playing with a TDS level around 90-140ppm, with hardness around 3-5 grains

    Comment by Martin — August 7, 2012 @ 9:17 am

  4. Excellent, Martin, thanks for the advice. When it comes from an expert who works for 3M, you can take it to the bank!

    Comment by Marc Wortman — August 9, 2012 @ 1:59 am

  5. While looking at high end built-in coffee maker, saw that manual states “Do not use water from reverse
    osmosis units. This could damage the appliance.” When I asked for more, I was told the lack of mineral content leads to “leaching” of minerals elsewhere, IE from machine parts into water to your coffee – eek.

    Comment by Anonymous — January 19, 2015 @ 12:24 pm

  6. Wow! I’ve never heard this before, but this is definitely good information to have. I will assume that the same advice applies to using distilled water. Very interesting.

    Comment by Marc Wortman — March 10, 2015 @ 6:35 pm

  7. “anonymous” is absolutely correct, but the damage is to your brewer. Long term use of RO water will damage metal components, e.g. heater. This process attempts to rebalance resulting acidic water that RO produces (nothing harmful is leached into the coffee). Fact is RO water is about the worst you can use to brew coffee. There are many articles available explaining the details why this is so.

    Comment by Ed — April 28, 2016 @ 7:23 pm

  8. Excellent information, Ed, thank you! I have not tried this water for brewing coffee, and am the opposite of an expert on the subject.

    Comment by Marc Wortman — April 28, 2016 @ 7:36 pm

  9. I have an acidic condition and am always looking for ways to take the acid out of coffee. Yesterday I tried The Toddy Brewing System using RO water. Unfortunately, the results were terrible. The coffee had a very sour taste. I had to pitch the whole batch. I have used this system before with favorable results.

    Comment by donna — May 7, 2016 @ 10:16 am

  10. Donna, any chance it is due to the RO water? Have you tried using the Toddy system with regular filtered water? – I ask because I’m getting ready to purchase one for the first time.

    Comment by Marc Wortman — May 10, 2016 @ 12:47 am

  11. I ordered a technivorm moccamaster and it said in the warranty that it did not cover it if you use osmosis water. I had to send it back since it is over $300.00.

    Comment by Cecilia Bruck — October 29, 2018 @ 1:41 pm

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