I bought this less than a month ago. Supposedly the filter for 23cup ZeroWater should last 40 imperial gallon. I agree that if in the place where I live the water is hard, it should last shorter, but I don't think we had even spent 20 Imp Gallon in my house as we are 2 of us when we work full time Monday-Friday and we don't arrive home until late. Plus we cook with mineral water, not even using this one for that.
tastes amazing, but very expensive filters.