ReplacementBrand RB-S1 Comparable Filter for the Pentek S1 and Culligan S1A Model Comparable to the Culligan-S1A and Pentek-S1 Water Filters Fits in other brand housings that use the standard 10 x 2.5 inch filters Lasts for 6 months or 600 gallons Reduces Sand, Soil, Silt, sediment, and rust Nominal 20 Micron Pleated Cellulose Water Filter