The rechargeable softening filter cartridge (Part # : 50511) is filled with the same resin that’s in a home water softener, and it’s just as effective. But because of its small size, it's lifespan is limited. On moderately hard water a new cartridge has about a 90 gallon capacity before it begins to “leak” hardness.

The good news, though, is that you can renew it through an easy, inexpensive process, that will last virtually forever!

Here’s how:

Buy a bag of standard water softener salt. It usually costs less than $10 for a fifty pound bag. It’s sold in Sears, feed stores, home stores, and large discount stores such as Sam's Club and Costco.

Pour a generous amount of softener salt into a large pan or bucket. Fill the pan with water until it covers the salt. But don’t overdo it. You want to make some very salty water.

Put your spent softening cartridge into the pan of salty water and let it sit at least overnight. (It won’t hurt it to stay there indefinitely, so you might just store it there between car washes.) The salty water, brine, will dislodge the calcium (hardness) buildup on the resin and replace it with sodium.

You might consider buying a spare cartridge or two so that one can be recharged while another is in use. If you keep one cartridge stored in the brine you can always have a recharged unit handy. Just swap out the one in the filter case for the one stored in the brine and your set to go! The useful life between regenerations, of course, depends upon the hardness of your water.