The SWC-25-2001 string wound filters are a cost-effective solution for the reduction of sand, silt, rust, dirt and scale particles. Hydronix string wound filter cartridges are made from 100% polypropylene cord. The Hydronix SWC-25-2001 filter cartridges are suitable for residential as well as commercial applications. This Hydronix polypropylene string wound filter is a comparable replacement filter for 20-inch standard water filter housings. The SWC series filters are suitable for both well and municipal water. The Hydronix string wound water filter should be changed when a decrease in pressure is noticed. Not intended for use with water that is microbiologically unsafe.