RO/DI units produce several times the amount of waste water as purified water. I'm getting 3 to 5 times as much waste water. I have no idea though how much minerals and salt are in the waste.I can't imagine that a gallon of saltwater a day or 30 gallons at once in a month would impact the trees or downstream neighbors anymore so than the salt that's put on the roads in winter does. But I could be wrong. I plan to have a plumber take a look.