This our replacement filter set for Watts WP-5 RO drinking water system.  Most reverse osmosis filter sets should be changed once per year.  Depending on your water quality, filters generally get dirty and should be replaced in order to keep your membrane working properly, and keep cleaning contaminants out of your drinking water.  The membrane is not included in this set but you can add it to your order by selecting it as on option.  It's recommended because you should change membrane every 3 years or sooner if your water quality is poor. A sanitizer kit is also available as an add-on option as well.  When you change your filters you should sanitize your systems before replacing them, to help keep the system clear of any harmful bacteria. Filter set includes: (1) 5 Micron Sediment Cartridge Filter (2) 10 Micron Carbon Block Cartridge Filter (1) 10" Inline GAC Cartridge Filter (1/4" Female pipe thread)                  Membrane is not included in this set, you change membrane every 3 years