Some 30 minutes earlier, Anthony Weyerman, a 17-year-old junior at Wahtonka Community School, had filled his hand-made solar water purifier with a few gallons of water from a hose.

Already, as he explained his project to a reporter, it was functioning as intended: The sun’s heat was evaporating the water, where it rose up in a mist and formed fat beads of water on the glass lid.