Is It Safe to Reboil Water?

You may have heard that is is unhealthy to reboil water or even to boil it away when cooking. Unless your water is exceedingly pure, reboiling water drives off the gases dissolved in the water and evaporates away some of the water, concentrating minerals and contaminants. There are two safety concerns with reboiling water. The first is that reboiling water increases the chance you'll get burned. With the gas bubbles removed, reboiling water can cause it to superheat and suddenly splash out when disturbed. The other safety issue concerns the chemical composition of reboiled water.