C&EN talks with Tzahi Cath, environmental engineer

With population growth and climate change both stressing freshwater supplies, demand for the precious resource could exceed supply by some 40% by 2030, according to a 2016 United Nations estimate . Growing up on a farm in Israel, Tzahi Cath became attuned to the problem of freshwater scarcity. Reusing water is a cause that he now champions professionally. As part of his PhD project, Cath worked on ways to supply water to astronauts on a potential mission to Mars. One hundred forty million miles from home, the astronauts on Mars would have to use the same water they’d brought from Earth over and over again—including that from their toilets. On Earth, such drastic measures might not seem necessary, but highly water-stressed areas such as Singapore, Southern California, and Texas are already reusing their wastewater to varying degrees. In 2019, the Colorado Springs Utilities approached Cath and said they wanted to