Gone through several filters now and always gets down to 0 ppm where a new Brita filter gets down to 70 ppm.  We have a family of 7 so we go through alot of water and the filters last about 2 - 3 weeks for our heavy usage (we use the Brita to get our water that starts at 125 ppm down to 70) then pour it in our Zero.  You'll need to keep an eye on the ppm because after you get to the recommended change out level of 6 ppm it will go fast to above this and the water will start getting a fishy smell.  We usually can tell when to change filters when the smell starts coming on.  I'd give it 5 stars if the filters lasted a little bit longer.