Water Pasteurization Indicator (WAPI)
Fred Barrett and Dale Andreatta
A wax-actuated thermometer that indicates when water has reached pasteurization temperature.
The Water Pasteurization Indicator (WAPI) is an open-source hand-made thermometer that indicates when water has reached pasteurization temperature and is safe to drink. Rather than waiting for water to boil (which occurs at 100 °C and is far beyond the required temperature for destroying microorganisms), a WAPI uses a melting wax to indicate that water has reached 65 °C. This saves fuel by eliminating the need to boil water to ensure that the pasteurization temperature has been reached.
Other temperature indicators such as candy thermometers.
Goal 6: Clean water and sanitation
Households (particularly those who typically boil their water)
WAPIs are built using openly available instructions that require the following materials: Polycarbonate tubing (3/8” OD, 1/4” ID), wax (Myverol 18-06), a washer (18-8ss, 1” OD, 3/8” ID), 2 single barrel compression sleeves, and a wire “S” hook.
Components must be locally purchased
Wax must melt at 65 °C.
Treated water should be stored in a clean container to avoid recontamination. Pasteurization does not treat water contaminated with salt or other chemicals.
Solar or biomass-powered pasteurization.
Rolla, T.C., Sun and water: an overview of solar water treatment devices, Journal of Environmental Health, 1998, 60(10).
“The microbiology of solar water pasteurization, with application in East Africa” a report by WAPI designer, Robert Metcalf
Safapour, N., Metcalf, R.H., Enhancement of solar water pasteurization with reflectors, Applied and Environmental Microbiology, 1999, 65(2), 859-861. (this study uses the WAPI as an indicator for pasteurization)
Solar Pasteurization, A chapter in Drinking Water Treatment by Ed Pejack (pages 37-54)
Kang, G., Roy, S., Balraj, V., Appropriate technology for rural India – solar decontamination of water for emergency settings and small communities, Transactions of The Royal Society of Tropical Medicine and Hygiene, 2006, 100(9), 863-866.
Pasteurizing water can reduce microorganism concentration to levels recommended by the WHO.
WAPIs have been evaluated and shown to reduce microorganism concentrations when the wax melts at 65 °C. Additional field tests and user reports have shown their durability and usability.
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