At a tech fair in Lembata, a volcano-sprinkled island near the eastern tip of Flores, Indonesia, 62-year-old subsistence farmer Daprosa and her friends Maria and Yuliana are checking out a water filter. It’s a simple $15 contraption, made of two plastic tanks with a ceramic-and-silver dome connecting them. The top tank is filled with river water and left overnight, with harmful chemicals and parasites removed as it trickles through. These women aren’t the only ones wondering about its success; local officials are interested, too — they want to know whether a giant version could be used to create a centralized water supply for villages.

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