Sediment Filter: This filter is used in the Athena only. It is the filter in position #1 in your Athena (it goes inside the left filter housing door). Unlike the original #1 filter for the Athena, this is a fiber filter that removes particulate, protects and extends the life of Filter #2 far better than the original, carbon-sediment filter for the Athena #1 spot. It also protects the life of the solenoid valve inside of the water ionizer. In water treatment all sediment filters have ratings expressed as either nominal (typical pore size) or absolute (all pores size at or smaller than). With 50 times the filtration capacity the new filter provides 1 micron absolute filtration. The filter life indicator on the Athena will monitor the life of the filter and should be replaced when the digital display for Filter #1 reads 9999. The filter-life in gallons is about 1000 gallons [longer filter-life than the original Athena #1 Sediment Filter that comes in the Athena ionizer.