Water Pasteurization Indicator (WAPI)

The Indicator is a simple device that uses the melting point of a special kind of soy wax as an indicator for water pasteurization.

WAPI diagram

The heating of water or milk to kill disease-causing organisms is known as pasteurization. A temperature of more than 65°C is sufficient for the elimination of microbes, including E.coli, Rotaviruses and Giardia the Hepatitis A virus. The Indicator is an enclosed tube of transparent plastic that contains a special kind of soy wax, which has a melting point of exactly 65°C. The tube is attached to strings so that it can be hung from something and dropped into the heating liquid. When the distinctly colored wax is observed to be melting, the water has to be left for only a few more minutes in order to be sure it is pasteurized.

The device is especially useful for solar cookers, and has been employed by the Aquapak, a low-tech water pasteurization device.