I have a reverse osmosis and deionization unit that filters my tap water from 450PPM TDS to 0 PPM TDS. I have had it for about 3 months and my TDS reader is now creeping up to 3 PPM.

I was considering waiting until the TDS reader gave 10PPM to determine the amount of chlorine it in, and then decide on that result whether I should purchase new filters at 10 PPM every time in the future.

If I knew at what PPM of chloride causes adverse affects on the homebrew, I would be able to better estimate when I need to buy replacement filters.

  • Lessons learned from a brief stint working in filter development: 1. TDS measures total dissolved solids, as stated in an answer below. To measure chlorine reduction, you'll need a spectrophotometer and free available chlorine reagent, and you'll most likely want to test in accordance with NSF Standard 42. Very cost-ineffective for home brewing. 2. Follow your filter manufacturer's recommended life span for filter replacement. Provided you're using a trustworthy brand of filter, there is a lot of good test data validating the recommended life span.
    – Grafton C.
    Dec 29, 2015 at 20:43
  • Similar to: homebrew.stackexchange.com/questions/13398/…
    – Philippe
    Jun 15, 2017 at 20:32

1 Answer 1


TDS meter won't detect chlorine even at swimming pool levels. Total Disolved Solids are your salts, metals, minerals. RO systems do strip the chlorine though.

RO water even with 10ppm tds will have no discernable flavor in beer.

But keep in mind, many beer styles like salts. RO IS always a good start for any water profile.

Chlorine is volatile so leave it in an open container a couple days to get rid of chlorine if you don't have a filter system.

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