I have bought replacement cartridges from Haferman Water Conditioning, Inc./ Kinetico on numerous occasions. I usually just go to their shop to purchase them. My original water softening system has just kept chugging along, and it knows when to recycle, so there has not been much occasion for them to come out and service anything for me. However, I once bought the wrong cartridge for the one under the sink, and they did come out to put a new one in for me. I thought that service call went well.