Originally Posted by hops2it
Well I tested my store's RO water. It had no real measurable alkalinity or hardness (via titration), but it shows 82 TDS. Sigh. Not sure how important that is in the grand scale. If the hardness and alkalinity are knocked out, should I still care about TDS?
Its probably still better than the tap water. The lack of hardness is not a surprise since the divalent Ca and Mg ions are preferentially removed from the product water by the RO process. If the local water is really hard, the machine may also have some sort of ion-exchange pretreatment that takes out the Ca and Mg and inserts Na or K. The RO product water has somewhat high Na or K. But given the TDS reading, the Na or K probably isn't that high to make it unusable. 82 ppm is not good, but its not a disaster. Do keep an eye on the reading and contact the machine operator to complain that the machine is not producing RO quality water.