Sediment water filter exclusively used in the Athena only. It is the filter in position #1 in your Athena (it goes inside the left filter housing door). It is a fiber filter that removes particulate. 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 1 micron absolute filtration this new and improved sediment filter is capable of filtering out contaminants up to 5 times smaller than that of the original filter. The filter life indicator on the Athena will still continue to monitor the life of the filter and should be replaced when the digital display reads 9999, after approximately 500 gallons have run through the filter. A modified filter stand is included with your order to replace the filter cup in use in Athena models sold prior to August 2009.