A friend asked me to look at her water heater that has a white mineral build-up on top. A plumber told her that it was because her chimney was inadequate and so the heater was not venting properly, so she called me. Using an incense stick while the water heater was running, I found that it drew the smoke very well. I found that a fitting was seeping (damn, i didn't check to see if was the hot or cold) and there was a layer of mineral on top that looked like the salt flats. I tasted it, and sure enough it was SALT. She does not have a water softener, and never has. She can offer no explanation as to why there should have been any salt in the vicinity of the water heater. It was installed in '94, is dripping at the drain, and purportedly pops and carries on while heating (though not while I was there) so it might as well be replaced, but what's up with the salt? PS Our local water supply is notoriously hard, but I've never heard of salt in the water.