A Water Pasteurization Indicator (WAPI) is a simple thermometer that indicates when water has reached pasteurization temperature and is safe to drink.
Pasteurization destroys all microorganisms that cause diseases from drinking contaminated water and milk. A small polycarbonate tube 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.
Since water pasteurizes at temperatures well below the boiling point of water, WAPIs save time when solar pasteurizing, and save fuel when using traditional fuels.