In many parts of the world, the sun is used to disinfect water.
By leaving a PET plastic bottle out in the sun for several hours, the sun's UV rays are utilized to disinfect water for people in developing countries. While this method has been approved by UNICEF, Red Cross, and the World Health Organization (WHO), the problem is knowing just how long to leave the sun-bathing bottle as the process can take anywhere from 30 minutes to two days, depending on the climate.
Wadi is coming to the rescue. It's a device, developed by Martin Wesian, that calculates when water is disinfected. Using solar power, it takes the place of a traditional bottle cap.
Step 1: You leave the bottle out in the sun.
Step 2: Take note of the progress bar -- a sad face means the water is still dirty.
Step 3: Happy face? The water is clean!
According to Fast Company, Wesian is working toward lowering the cost of Wadi from $13.50 to $10 or less.