"stone breaker", is that right? And you would be using it to help with breaking up gravel in the kidneys? Or gallstones? Since this is the water-only forum, I think you can guess what the standard answer might be. :-) The reason for the water only is that it puts the body into a deep cleansing mode, puts the digestion on serious holiday, whereas anything of foodstuff or nutrient content that goes in, tells the body is it still 'eating', albeit not eating much. "starving", some people might call it. I'm on the fifth day of a water fast. On my 29 day fast (confession here) I had a small amount of red wine on the first three nights. Probably sounds crazy, but it helped me over the intitial low-grade panic of adjusting to water only.
I can only say, go with your best intuition. You must be sensing you need the chanca piedra? Only you can best know your own body.