Originally Posted by craq5
So with RO water do what parameters do I enter in the EZwater spreadsheet? Sorry if this is a dumb question.
Not at all. Zero will do and is easy to remember. My experience with these systems used for brewing is that they go on for ever before the membrane begins to degrade. When I upgraded I gave away a system that I had been using for over 10 years that still performed well but you may wish to check up on the performance of your system from time to time with an inexpensive 'TDS' (in quotes because they measure conductivity, not TDS, though they read in TDS) tester. For example my system typically reads 3 ppm out and 160 in meaning the average rejection is about 98%. This system is about 3 years old though, because it is used mostly for brewing it only has about 200 hours on it. In the columns below I've taken your analysis and applied 90% and 95% rejection to the concentrations.
0% Rejection-------> 90% - 95%
Sodium 63 ppm ---> 6.3 - 3.1
Potassium 3 ppm ----> .3 - .15
Calcium 34 ppm ----> 3.4 - 1.7
Magnesium 15 ppm ---> 1.5 - .75
Total Hardness 148 ---> 7.4 - 3.7
Sulfate 75 --------------> 7.5 - 3.8
Chloride 75 -------------> 7.5 - 3.8
Total Alkalinity 99 ------> 10 - 5
A new system is going to reject more like 98% so the numbers show that even with a conservative assumption of 95% treated water is essentially mineral free in your case.
Something to consider both WRT membrane life and rejection is the fact that your water is super saturated WRT calcium carbonate and magnesium carbonate (you don't say what your pH is but I'm guessing it's about 9) which will precipitate on the membrane of your filter shortening its useful life. To avoid this RO units are fed with softened water (or run at very low recovery but in your case no level of recovery will save you). Using a softener replaces magnesium and calcium with sodium with the result that your water softened would contain an additional 67 mg/L sodium which, with the 63 mg/L already in the water would total 130. At 90% rejection you would have 13 mg/L sodium and at 95% half this (6.5). But membrane manufacturers are aware that RO systems are often used this way and strive for good sodium rejection. Often you will see the spec sheets listing sodium rejection at about 99%.