I recently started using RO water produced from this thing:

Countertop Portable Universal 5-stage Reverse Osmosis RO Purification Water System

Countertop Portable Universal 5-stage Reverse Osmosis RO Purification Water System with DI Deionizing Mixed Bed 0PPM postfilter

The TDS meter (cheap amazon thing) reads 0 ppm. I used Bru'n Water to create a water profile for a Kolsch 15 lb pils, 8oz flaked wheat, 3 oz Acid Malt. Added 2.5 grams Calcium Chloride to mash water of 5.7 gallons. Bru'n water had my PH target at 5.41, but actual PH was closer to 5.1, and I had to tweak the mash with some pickling lime to reach 5.3. Ph meter is a milwaukee ph 53 and I calibrated to 4.01 solution, also chilled mash sample to room temperature.

Is this low PH common using RO water? I know there are lot's of variables here (malt, strength of acid malt etc...) but am I missing something big or is this sort of thing common? Am I just going to have to keep good notes and work it out? Any pointers or a sanity check of yea..well that's what you have to do would be helpful.

  • Could be that the acid malt was stronger than Brun' water predicts. So I'd say yes you are going to just need to take good notes. At least you have a pH meter while doing this. Most people don't have one and think they can dabble in water chemistry without it.
    – brewchez
    Jan 22, 2017 at 1:34
  • Bru'n water has an acid malt strength setting and I was able to bump it up to 2 which more closely resembles my measured PH. Still a little high but at least closer to reality. Thanks for that idea.
    – Pale Ale
    Jan 22, 2017 at 14:58
  • I don't see how you could with any confidence say that your acid malt was stronger than expected given that any other number of factors such as mismeasuring salts/grain/water, incorrect meter calibration, etc could also account for the variance. Bah, this reminds me of why I gave up on water chemistry!
    – GHP
    Jan 27, 2017 at 19:50
  • I tried as best I could to convey that I measured everything carefully. The grain bill is pretty simplistic so I thought it was worth a shot at some folks with experience to help set me straight. I may start doing a small test mash to verify my assumptions. I'm in the ball park and so far the results are awesome but I want it totally dialed in.
    – Pale Ale
    Jan 30, 2017 at 16:28

2 Answers 2


I would expect RO water to lack the carbonates to buffer your mash pH. The water I tend to brew with has pH 7.2-8.0 mean 7.61 depending on time of year and a hardness as CaCO3 of ~270 ppm. This offers a fair amount of buffering. As you are only adding calcium chloride to the solution and no carbonate I am not surprised that your pH is more acidic than anticipated.

I have personally never used the Bru'n water calculators myself, I tend to use good old trial and error, and dial in with a tweak here or there as required to get the number lining up.

Regarding pH meter calibration, it is usually best to calibrate with 2 separate buffered solutions one acid and one neutral or base.

Reading a few posts on other homebrew forums, many of them suggest using 50/50 RO/tap water to balance out their brews, or 60/40 40/60 depending on the target I would suggest trying this, as it will leave trace level of other salts in there.


Your ro water shouldn't effect your ph also you can do a quick purity test with a multimeter set it to the mega ohms range and keep the probes about a cm apart they should read about 18Mohm. If that's the case you will have very pure watter.

  • Water most assuredly affects pH. The ions in solution that you are testing for with a multimeter buffer changes in H+ or OH- Feb 23, 2017 at 4:18
  • While you are correct that RO water will not have any of the salts in it to provide PH buffering in the event of acid/base additions the RO water itself is PH 7 and will not move your PH down as the questioner was asking. In addition, the salts commonly used by brewers (gypsum/chalk etc) will provide you with buffering at least as well as water from a tap would assuming you are not using very hard water in your other samples to begin with not to mention that dissolved organics and salts from the barley will add additional buffering compounds to your wart.
    – Gremwatch
    Feb 25, 2017 at 3:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.