I would think after many soakings with hard water that the stone would retain minerals, as to what grit those deposits or effects on the hone, I have no clue. I am in TX for a while and the water here is nasty, mineral deposits on everything, shower heads clog, the dishwasher needed a few vinegar treatments to work right...a good question.

I know my norton 4k/8k is a thirsty one and am sure that stone has plenty of absorbed deposits by now. I imagine after a few years and a few hundred soakings it could have an effect but I don't worry about it, I will be rolling out of here soon enough.