I am cutting the tap water with RO water to reduce the amount of Nitrate in my water. I live in an area with a lot of farming around it, and in the summer time when the water tables get low the nitrates can get has high as 50ppm. Right now, my nitrates out of the tap run about 20ppm. The tap water runs about 3 degrees of GH and KH. I basicly use the tap water to stretch my RO water supply.