Filter replacement depends on varying factors such as the incoming water quality and usage. In general, no carbon filter should stay in service for more than 12 months. Sediment filters are generally changed twice as often as carbon filters. Sediment pre filters are much less expensive and their function to catch the sedient before it plugs the more expensive carbon filter. So it is proper maintenancce to change the sedimenet pre filters twice as often as the carbon filters. Bad water conditions and higher usage can cause the need to change the filters as often as every 3 months.