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JOE HARRISON/WQA POSITION ON RO WATER----- Original Message ----- Peter: We still use the "Consumption of Low TDS Water" Report. It might date us, but as I like to say, good science never dies. It is still true that low TDS water has no ill health effects. Regarding aggressiveness of whole-house RO treated water, there is not a black and white line between aggressive and not aggressive. There are municipal water supplies that deliver tap waters comparable to the product water from RO treatment of mineralized well waters. Tap water in Seattle, Tacoma, and Portland, for example, I believe is at about 30 mg/L of TDS and zero water hardness. The rule of thumb that I advise is that RO product water doesn't become untenably corrosive toward the dissolution of copper until the product water TDS drops to single digits (below 10 mg/L). However, 20 mg/L TDS is more aggressive (corrosive) toward copper than is 50 mg/L, which is more aggressive than 100 mg/L, etc. If copper is being dissolved, a polyphosphate feed will lay down a better passivating film on exposed copper surfaces than will hardness scale. Joe |