A Water Pasteurization Indicator (WAPI) is a simple thermometer that indicates when water has reached pasteurization temperature and is safe to drink. The WAPI is a small polycarbonate tube that contains a wax that melts when water or milk is heated enough to be pasteurized (65 C/149 F). This saves much fuel by eliminating the need to boil water or milk to ensure that the pasteurization temperature has been reached.