Las Vegas isn’t just a hot spot for revelers. Thousands of businesses, particularly from California, have moved to the region over the past few decades, and the population is booming alongside other Southwestern cities. All of that growth in a region plagued by extreme heat, drought, and a dwindling water supply raises tough questions for city and state officials who want to spur economic growth without draining the Colorado River dry. In one example of that challenge, Arizona’s governor in June halted construction in areas around Phoenix, citing a lack of groundwater.