After a breathless trek up a steep Andean mountainside, Javier Antiporta crouches beside a tiny spring and carefully lifts a fine screen out of the water. He hopes the delicate filter yields clues about whether water seeping through the ground was channeled by a canal system farther uphill that was probably built even before the Incas ruled the land now known as Peru. Those canals—which allowed ancient inhabitants of the Andes to maintain a water supply during dry months—could also help ensure a steadier flow of water to Lima, the parched Peruvian capital, some 80 miles away on the coast. With Lima’s population expected to swell to more than 13 million by 2040 and glacial water sources threatened by climate change, the city’s... [Log in to read more]