Watts Premier WP105341 RO Pure Carbon Post-Filter, 12 x 2.5&quot, Plain Drinking water enters this filter after the water storage tank and it is used as a final polishing filter to crispen up the flavor and enhance the taste of the water. Easy filter maintenance, with the unique swivel-valve, push-button assembly allowing for one-step filter changes that doesn't require shutting off the water source The 105341 Carbon Post-filter is designed for use with Watts Premier's RO Pure (531407, 531411) Reverse Osmosis Systems and is compatible with the RO Pure Plus (531417) and Zero Pure Plus (531517) Reverse Osmosis Systems For system top performance it is recommended to change out the carbon post-filter every 1 year or 600 gallons