I know I have posted this in the past but we now have done a long term test on the RO dispensers in the stores. We have found that most of the time it is not RO water. Sometimes as high as 200 ppm. Members of our brewing club and I have purchased TDS meters and test on a regular basis.
Out of 6 dispensers we test only one was under 50 ppm and that soon went up.
If you are using this kind of RO water and entering 0 in your water calculations and still have what seems like water problems this might be a good place to look.
This warning goes to anyone using RO water since you usually can’t tell from taste or appearance that the water is not low TDS as it should be. Even if you have your own machine at home, be sure to have a TDS meter and check the RO water to assure that it has the low ionic content that you expect and want.
TDS meters are cheap and reliable…GET ONE!
So the store bought gallon jugs of RO water?
I have started using bottles that specifically say “distilled” on them to compliment my tap water at home. Hopefully I am good 
[quote=“Templar”]So the store bought gallon jugs of RO water?
[/quote]
OK, good point. Hopefully if someone is selling RO in jugs, they are keeping an eye on the quality of their product. It’s the RO machines at the grocery stores and in our homes that need a watchful eye too.
I have been using water from my local Walmart water machine. I just tested it and it is 31ppm. I never thought to test it I just assumed all RO water was created equal
I just bought a TDS meter recently to check the quality of my home RO system. I needed to change the filters. The TDS was 57ppm. Now after changing filters and membrane, it’s down to 7ppm. Not too shabby. It’s not the best RO system available, but I think that’s good enough.
Martin, what is the upper level of ppm that indicates you should change your filters? 20? 30ppm? I see referenced that you should change the stage 1 and 4 filters every 6-12 months all the time, I just wonder what ppm I should be looking for to gauge when they need to be changed.
I have an in-line TDS meter on my RO system and I notice that the TDS reading rises when there isn’t much flow in the machine. So don’t get to bent out of shape if you see a reading above 50 ppm. Draw more water out and see if the TDS is reduced. By the way, even at 50 ppm TDS, the levels of the individual ions are still very low and acceptable for brewing. The main question is: which ions are high??? Its usually the monovalent ions such as Na, Cl, and HCO3. That last one is the troublemaker!
But, I suggest that you should be getting ready for a membrane replacement if you see consistent TDS over 50 ppm. That is clearly beyond what a well-performing system should produce. Be sure to replace that carbon filter with a new carbon block filter, since chlorine compounds are the primary reason why a membrane fails.
Thanks, Martin. Great advice, as usual! I guess I’ll go with the recommended replacing of the carbon filters (stage 1 and 4) every 6-12 months, then keep and eye on TDS from there to check the membrane.
Unless you are treating a huge amount of water, I can’t imagine that the carbon pre-filter needs to be changed that often. If that is a carbon post-filter, you probably don’t have to ever replace it since it doesn’t do much.
[quote=“Templar”]
I have started using bottles that specifically say “distilled” on them to compliment my tap water at home. Hopefully I am good [/quote]
Me too.
