Water Pasteurization Indicator

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A WAPI or water pasteurization indicator 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.

Two recently-developed Water Pasteurization Indicators (WAPIs) are being explored for feasibility. Like current WAPIs available through Solar Cookers International, these models contain a special wax that melts as water is pasteurized, providing a visual indicator when heated water is free from disease-causing organisms. Since water pasteurizes at temperatures well below boiling, WAPIs save time when solar pasteurizing, and save fuel when using traditional fuels.

1 New designs explored
2 Information from Robert Nepper on the construction of the new Cool WAPI
3 Audio and video
4 See also
5 External links

[edit] New designs explored

End plugs are hammered in, eliminating the melting step

The first prototype, from current WAPI makers North Star Devices, is similar in design to current WAPIs in that it is comprised of a wax-filled polycarbonate tube strung with a fishing line and held low in the water with a metal washer. The current WAPI, however, requires that the ends of the tube be melted and pinched - which can be a difficult and slow process - while the new design does not require any heating. Instead, tight-fitting plugs, pre-drilled for fishing line, are hammered in to each end of the tube, sealing in the wax.

The assembled WAPI, strung with fishing line and washers

The second prototype was designed by a group of students at Ohio State University (USA) using wax-filled glass capsules from Solar Solutions, makers of the AquaPak solar pasteurizer. Under the direction of Prof. Dennis Guenther, these students - Arif Mohsin, Zaidi Ahmad Latiffi, Khairil Azim Khairuddin, William Hunter, Shimpei Narita, and Muhammad Yusoff Che-Lah - developed a unique spring and rod system to hold the capsule upright in the water and keep it near the bottom of the pot or jar. The middle seven coils of stainless steel spring, with an inside diameter slightly smaller than the outside diameter of the tube, firmly holds the capsule in place.

A coiled wire and inserted rod allows for adjustable WAPI

The three coils on each end of the spring are bent perpendicular to the capsule in such a way that a stainless steel rod can be slid through them with a tight fit. The capsule can then be slid up or down the rod as needed. [For further information see Final report on possible improvements to the WAPI.]

[edit] Information from Robert Nepper on the construction of the new Cool WAPI

Regarding the new Cool WAPI, we call it “cool” since it requires no heat for assembly when compared to the earlier version WAPI. We have re-designed the WAPI in response to customers who wanted it capable of being assembled in the country of use. We offer it in the completely assembled version and in the totally unassembled version, complete with all parts.

Yes, unskilled persons can assemble the new cool WAPI with a minimum of tools and instructions. All that is really needed is a common claw hammer and a heavy, flat rock, a cement block or an anvil. It must be solid and heavy or you will find it too difficult to hammer in the plugs.

To prevent injured fingers, however, we offer a free simple holder set with purchases of 100 pieces or more. The holders also prevent the plugs from being driven in too far (obscuring the holes needed for the fish line).

We sell the completed version for $1.15 each and the unassembled version for $.95 each (in lots of 100 or more). There is quite a bit of manual labor in making the plugs and the wax slug so we cannot offer volume discounts at this time. If the volume gets higher, we will make them with more automation, hopefully to be able to reduce the price and offer volume discounts as well. For more information, contact Robert Nepper.