The lifetime of our filters varies depending on the type of media and the amount of media inside. We recommend that the filter should be replaced after so many gallons or so many months for its best efficiency. Once the media has run its course (filtered out the bad chemicals from the water), then it’s time to replace the new one. For example, our most common triple units have three different filter sections:Aquaspace Compound (AR-100) is rated for 12 months or 1,000 gallons (whichever occurs first)Fluoride & Heavy Metals Compound (AR-100F) is rated for 6 monthsMicrobial Reduction Ceramic Filter (AR-900C) is rated for 24 months or 50 cleaningsA good comparison would be the oil in a car. While the oil in a car does not “run out” like gasoline does, it continues to travel through the engine until you have traveled X number of miles or X number of months and it needs replacing. Same with our filter media, which is designed to be replaced at a specific time to ensure optimum quality.