Sunlight/UV-light dose indicator

The Challenge

Diarrhea is the second biggest cause of deaths of children under five years of age worldwide: every year, more than 1.5 million children die because of diarrhea, which often is caused by the consumption of water contaminated with micro-organisms. Purifying (disinfecting) contaminated water therefore becomes a major venue for preventing diarrhea and other waterborne diseases such as cholera or dysentery.

Currently, more than 3 million people in low-income countries worldwide are using solar water disinfection (SODIS) for purifying their drinking water, with the method proven to be simple, low-cost, and appealing to consumers because the water does not change its taste. However, further promotion of solar water disinfection has been slow because the efficiency of the method is not intuitive: no change in the water quality is visible to the consumers.

The Challenge, sponsored by The Rockefeller Foundation, was to overcome this limitation by developing an indicator which gives a visual signal to the user when the process of solar water disinfection has finished – that is, that the water has been exposed to a sufficient dose of sunlight and therefore is safe to drink.

The Solvers

A team of four graduate students from the University of Washington -- Chin Jung Cheng, Charlie Matlack, Penny Huang and Jacqueline Linnes -- developed the winning solution. Linnes began working on the Challenge with Engineers Without Borders members Penny Huang, a senior in chemical engineering, and Chin Jung Cheng, then an undergraduate in chemical engineering and now a UW doctoral student in bioengineering.

At first, the students focused on developing a chemical test strip. Then they considered an electronic sensor and contacted Charlie Matlack, a UW doctoral student in electrical engineering. Together they built a system using parts from a keychain that blinks in response to light. Other electronics monitor how much light is passing through the bottle and whether a water-filled bottle is present, so the system knows when to stop or start recording data.

“It has all the same components that you’d find inside a dirt-cheap solar calculator, except programmed differently,” Matlack said.

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The Solution

The team's proposed solar disinfectant indicator is a self‐contained, self‐powered electronic device that is low‐cost, durable and reusable. Composed of off‐the‐shelf components and proven technology, the indicator should withstand 10 years or more of use. Having essentially no moving parts except a flexible bottle holder, the Indicator starts and stops operation automatically based on the presence of a filled water bottle.

The Realization

In addition to granting the Sodis Foundation a nonexclusive license to use their life-saving technology, Matlack, Linnes, and Tyler Davis have founded PotaVida, a nonprofit business to manufacture and market the device, either to users or to nonprofits that promote solar disinfection. PotaVida won first place and a $25,000 award in the annual University of Washington Business Plan Competition, which they plan to invest in distributing and promoting adoption of their solar disinfectant indicator.

“We will lower the cost to non-profits of providing safe water to people after disasters and in ongoing need scenarios. At a personal level, our product provides the visual feedback and guidance that people need to use a disinfection process which is otherwise invisible and impossible to know when done correctly,” said Charlie Matlack. “We’re at a point where we recognize the need for work on this beyond engineering, ultimately, the hardest part is going to be to get people to use it.”


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