The Colorado River Basin is inching ever closer to “Day Zero,” a term first used in Cape Town, South Africa when they anticipated the day in 2018 that taps would run dry. Lakes Powell and Mead, the Colorado River’s two enormous reservoirs, were full in 2000, storing more than four years of the river’s average annual flow. For more than two decades water users have been sipping at that supply, watching them decline. Long-term drought and climate change is making this issue potentially catastrophic. Today the entire Colorado River reservoir storage system is 2/3 empty. Moreover, federal officials project that within two years, the water level in Lake Powell could be so low that it would be impossible for water to flow through the dam’s turbine intakes. When that happens, it’s clear the dam will no longer generate hydropower, but it’s also possible the dam will not release any water at all. That’s because the only other way for water to move through the dam when the...