Updated on January 3, 2024


Created on August 9, 2017

Water Pasteurization Indicator (WAPI)


A wax-actuated thermometer that indicates when water has reached pasteurization temperature.

Developed By
  1. Fred Barrett and Dale Andreatta
Content Partners


Product Description

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.

Target SDGs

SDG 6: Clean Water and Sanitation

SDG 3: Good Health and Well-Being

Market Suggested Retail Price


Target Users (Target Impact Group)


Distributors / Implementing Organizations

Many organizations have made and distributed WAPIs including Agua Pura Para el Pueblo and Rotary International Clubs (such as Buford/North Gwinnett, Calabasas, and Monterey Sunrise).

Manufacturing/Building Method

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.

Intellectural Property Type


User Provision Model

Construction manuals and instructional videos for building WAPI’s are openly available online. Links can be also be found in Research & standards section.

Distributions to Date Status


Deactivation mechanism


Energy source


Manufacturer-specified water treatment rate (L/hr)

Not applicable

Bacteria reduction

6 log

Virus reduction

4 log

Protozoa reduction


Heavy metals and/or arsenic reduction


Maximum recommended influent turbidity level (NTU)

Not applicable

Effluent turbidity levels (NTU)

Does not reduce turbidity

Safe water storage capacity (L)


Design Specifications

A WAPI consists of Myverol 18-06 soy wax that is housed inside a sealed clear tube. When submerged in water with wire and washers, the wax will melt from one end of the clear tube to the other at 65 °C. WAPI’s are symmetrical and thus can be repeatedly used by simply flipping them over.

Product Schematics

Technical Support

None available

Replacement Components

Components must be locally purchased



Manufacturer Specified Performance Parameters

Wax must melt at 65 °C.

Vetted Performance Status

Water pasteurization is well known to be effective against microorganisms (bacteria, viruses, and protozoa). Specifically, the WAPI has been used by academic organizations to test water pasteurization in low-resource situations.


Treated water should be stored in a clean container to avoid recontamination. Pasteurization does not treat water contaminated with salt or other chemicals.

Complementary Technical Systems

Solar or biomass-powered pasteurization.

Academic Research and References

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.

N. Safapour and R. H. Metcalf, “Enhancement of solar water pasteurization with reflectors,” Appl. Environ. Microbiol., vol. 65, no. 2, pp. 859–861, 1999.

T. C. Rolla, “Sun and water: an overview of solar water treatment devices,” J. Environ. Health, vol. 60, p. 30+, 1998.

“WAPI Flyer,” Monterey Peninsula Sunrise Rotary Club. Available: http://www.montereysunriserotary.org/wapi-flyer.html

“Agua Pura para el Pueblo,” Aguapuraparaelpueblo.org. Available: https://www.aguapuraparaelpueblo.org/

“Water Projects,” FFYIA. Available: https://www.florenceforyouthinaction.org/waterprojects

“Water Pasteurization Indicator (WAPI),” Engineering For Change. Available: http://old.engineeringforchange.org/solutions/product/water-pasteurization-indicator-wapi/

“Multi-Fuel Water Pasteurization Indicator (WAPI),” Sun Oven The Original Solar Oven and Solar Cooker, 29-Apr-2020. Available: https://www.sunoven.com/product/water-pasteurization-indicator-wapi/

“Goal 6,” Sdgs.un.org. Available: https://sdgs.un.org/goals/goal6

“Agua Pura para el Pueblo,” Aguapuraparaelpueblo.org. Available: https://www.aguapuraparaelpueblo.org/?p=663

“Water Pasteurization Indicator,” Solar Cooking. Available: https://solarcooking.fandom.com/wiki/Water_Pasteurization_Indicator

“What is a Wapi or Water Pasteurization Indicator?,” Write Studio, 08-Oct-2012. Available: https://www.writestudio.com/304/water-pasteurization-indicator

“The microbiology of solar water pasteurization, with applications in east Africa,” Nocookie.net. Available: https://static3.wikia.nocookie.net/__cb20101207224924/solarcooking/images/a/a0/Granada06_robert_metcalf.pdf

Compliance with regulations

Pasteurizing water can reduce microorganism concentration to levels recommended by the WHO.

Evaluation methods

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.

Other Information


Comments from the Community


  1. Steve Harston says:

    It’s unclear to me how this product is intended to be used. Is it intended to be a stationary or mobile device? If it is a stationary device, what is the advantage of the GPS? This is probably a cool design feature but the value of it is not described anywhere. Is this cooler intended to be plugged into the wall the majority of the time with a battery backup? Is it powered by a solar panel? Is it completely passive where the ice packs are removed and frozen in an external freezer?

  2. Laura MacDonald says:

    •Rebranded to Safe Water Book
    •Also filtration? What is the primary mechanism – filtration or disinfection?
    •How do you have a “user provision model” already if it’s still a prototype?
    •Price not $0, not being sold yet
    •Any information on flow rate through the book’s page?

  3. Anna Murray says:

    Agree about confusion between filtration and disinfection as the method of treatment. It’s a little misleading to have this listed alongside disinfection products.

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