You only use the rock salt in the unit when you want to rejuvenate the
filter inside the unit. The you dump the rock salt out and its ready for
you to hookup your water source to go thru it.

Your water source hooks to one side and out theother comes the spotfree
water you use to rinse things down.

Thats the way I see it.

http://www.topoftheline.com/spotwatfil.html