The desert doesn’t look like it has anything to give. Then night falls, the air cools, and a quiet trickle of water begins to gather. That is the basic promise behind a new hand-held atmospheric water harvester built at UC Berkeley. It is a device that captures water molecules from air at night, then uses only ambient sunlight during the day to release that moisture and condense it into drinkable water. In tests in Death Valley National Park, one of the hottest and driest places in North America, the system kept working through wide temperature swings. It also functioned well with very low humidity. “Almost one-third of the world’s population lives in water-stressed regions. The UN projects in the year 2050 that almost 5 billion people on our planet will experience some kind of water stress for a significant part of the year,” said Omar Yaghi, a Berkeley chemistry professor who leads the work and is known for inventing metal-organic frameworks, or MOFs. “This is quite relevant to harnessing a new source for water.” The …