I'm a LMT, and I can't find anything in our state regulations (or any other state's regs) about this. I work with hot stones at a salon that specializes in hot stone massage, and I'm here to tell you that changing the water out and cleaning the stones between clients would be impractical. As far as germs go, the water that the stones sit in are is very hot (up to 130 degrees), plus we add an all-natural, mild antibacterial to the water/stones between clients. The water gets emptied at the end of the day and the stones and heating pot are throughly scrubbed with an anti-bacterial soap and sprayed with the all-natural antibacterial.