This filter system and replacement filters are supposedly rated for at least 500 gallons, and are to be replaced every 6 months. We use on average about 2 gallons of filtered water per day, so by rough calculation that would be about 400 gallons in 6 months. What frustrates me is that in the last 6 weeks of the 6 month cycle, the flow from the system becomes exceedingly slow, probably only 1/4 of the flow compared to a fresh filter. It gets very frustating waiting so long to get a glass of water.