The white stuff is probably lime scale, which is calcium carbonate.  

Several different kinds of kidney stones, but something like 80% most common are calcium oxalate stones.  Most common advice if concerned is to eat less oxalates, since calcium has important functions in the body in nerve impulse transmission/electrolyte.   Excess calcium leaves in your urine.

General drinking water engineering advice is just to soften your water to remove the +2 hardness ions, and not drink copious amounts of distilled or deionized water, as it attempts to mine ions out of your body.