Watts Premier (105351 RO Pure Carbon Pre-Filter (Yellow) Filters down to 5 Microns which is in the particle filtration category and is equivalent in size to milled flour 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 105351 Carbon Pre-filter is designed for use with Watts Premier's RO Pure (531407, 531411), RO Pure Plus (531417) and Zero Pure Plus (531517) Reverse Osmosis Systems For system top performance it is recommended to change out the carbon pre-filter every 6 months or 1350 gallons