Derry Posted January 30, 2010 Share Posted January 30, 2010 I've got a 4-stage Aqua-Pure undersink RO unit that's rated for 25 gpd. The stages are: Five micron sediment & rust filtration Activated carbon filtration Reverse osmosis membrane Final activated carbon polishing filtration What kind of results should I be able to expect in terms of final TDS? FWIW, my TDS going in is about 250. Quote Link to comment Share on other sites More sharing options...
DaJMasta Posted January 30, 2010 Share Posted January 30, 2010 I think that's typically 10-25 ppm or so worth of TDS, but if you added a DI chamber then you'd be at zero or at least less than 5 ppm for sure. The final carbon stage - at least as I understand it - is more for a decent taste to the output water when used in drinking systems than it is for reducing TDS. Provided of course that the membrane has a fairly high rejection rate and that it's kept in good working order. Quote Link to comment Share on other sites More sharing options...
Mike M. Posted January 30, 2010 Share Posted January 30, 2010 The goal is TDS=0 My guess since you do not have deionization after the ro membrane is that you'll end up with TDS 5-7. That's what I see coming out of my RO membrane prior to running through the DI resin. Mike Quote Link to comment Share on other sites More sharing options...
caferacermike Posted January 30, 2010 Share Posted January 30, 2010 I agree with the first reply of 10-25, even as high as 50. For a quick reference, figure out what brand your membrane is and it's rejection rate % compared to your incoming TDS. For example: Dow Filmtech 24gpd membrane states a rejection rate of 98%. Your incoming is 250x0.98=245 for a difference of 5TDS. In essence when new your meter should read 5ppm or TDS. Of course that is not an exact number so somewhere around there is what I'd expect to see. Quote Link to comment Share on other sites More sharing options...
JimD Posted January 30, 2010 Share Posted January 30, 2010 (edited) I dont know about 50 but 10-25 sounds about right. I guess it depends on the source water and the rejection rate of the membrane as Mikey said. My tds before DI is right at 12ppm. Also, if you plan to add DI, get a 1 micron sediment filter to help prolong the life of the DI media and RO cart.. Edited January 30, 2010 by JimD Quote Link to comment Share on other sites More sharing options...
offroadodge Posted January 30, 2010 Share Posted January 30, 2010 So i bet its even closer to this 9-13 TDS Quote Link to comment Share on other sites More sharing options...
+dapettit Posted January 30, 2010 Share Posted January 30, 2010 Add a DI cannister and DI resin (BRS) to the system. TDS=0 Dave- Quote Link to comment Share on other sites More sharing options...
caferacermike Posted January 30, 2010 Share Posted January 30, 2010 Yeah Jim my RO puts out about 40ppm, however that is because I have 480ppm incoming and I have 3 100gpd Filmtech membranes in a parallel configuration. They each put out about 15 but it adds up once it all meets and goes into the final 3 DI canisters. It is a very large 300GPD unit. Quote Link to comment Share on other sites More sharing options...
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