Biologically-contaminated water does not need to be boiled to make it safe to drink using a WAPI.
Contrary to common belief, according to Solar Cookers International Network, water only needs to be brought to a temperature that is sufficient to kill all disease-causing organisms.
This is known as water pasteurization.
Because the pasteurization temperature is much lower than the boiling temperature, pasteurization results in great fuel savings.
Since thermometers are not accessible to many people around the world, there is a need for a simple device that indicates when water has reached pasteurization temperatures.
Fred Barrett, who was with the United states Department Of Agriculture when Dr. Metcalf worked with him on a solar box cooker project in Sierra Leone in 1989, came up with the idea of using vegetable wax, with a melting point near 70°C (158°F), as an indicator.
He built several models based on the idea of wax inside a plastic cylinder, and successfully used them to verify pasteurization conditions of contaminated water.
In 1992, Dale Andreatta, a Ph.D. candidate in mechanical engineering at the University of California, Berkeley at the time, created the Water pasteurization indicator (WAPI) in its current form.
The WAPI (Water Pasteurization Indicator) is a reusable, inexpensive thermometer employing a plug of soybean wax, which melts at 68°C, just above the 65°C or 149°F pasteurization temperature for water or milk, at which point all disease-causing organisms (bacteria, viruses, and parasites) are killed.
Since the water is not heated all the way to boiling when using a solar oven, and merely reaches the pasteurization temperature, time is saved and less fuel is consumed.
The hydrogenated soybean oil (a food-grade emulsifier powdered wax) is encased in a small clear plastic tube, weighted with a metal washer.
Fishing line or wire suspends the WAPI toward the bottom of the water container (where the water is coolest).
The WAPI is oriented with the wax plug at its top, but after melting the wax flows to the bottom part.
Then the user can remove the WAPI by the string or wire without contaminating the clean water with the fingers as shown in the video.
Curated From Wikia Solar Cooking | Water Pasteurization
Get started making water safe to drink on your next outdoor or camping trip.
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