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.
Primary water purification method
Manufacturer-specified water treatment rate, measured in liters per hour
Laboratory-evaluated log scale removal rate of bacteria
Laboratory-evaluated log scale removal rate of viruses
Laboratory-evaluated log scale removal rate of protozoa
Reduction levels of heavy metals and/or arsenic through this treatment system
Manufacturer-specified maximum level of inlet turbidity (NTU)
Range or value of outlet turbidity levels (NTU)
Is there safe water storage integrated into this product?
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).
Metcalf, Robert, “The microbiology of solar water pasteurization, with application in East Africa” a report by WAPI designer.
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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