wlbadger, in my experience putting tap water through a brita does alter the hardness of the water slightly, but the main thing the filter does is take out most of the heavy metals and contaminants that the water authority pump into the supply to keep it safe for us. Remember there has got to be sufficient purification in the supply to dissapate veils disease. I try to use filtered water to replenish my tank. I find it rewarding even though its time consuming.