Bought a house that already had one of these installed with no cartridge installed. Because it was very rust stained and did not know how long it was installed I purchased a new one. After two days the filter cartridge was plugged and my water pressure was way down. When thru three cartridges in just over a week and ended up removing the filter and buying a new high end softener and my rust problem is solved. I am sure this filter works for low rust situations but if you have a lot of rust in your well system you will be changing cartridges every few days and that gets expensive and is a pain.