How Does a State Use 40 Percent Less Water? A recent study found that if the Colorado River drought continues, Arizona, California, and Nevada may have to cut their water usage by nearly half. Acceptance is the first step. Justin Sullivan/Getty Images A tall bleached “bathtub ring” can be seen on the rock around Lake Mead in 2015, where water levels have sunk lower and lower. Arizona, California, and Nevada will need to cut their use of Colorado River water by nearly 40 percent by 2050. A study by researchers at Utah State University, which the Arizona Daily Starreported this past Sunday, noted that Colorado, New Mexico, Utah, and Wyoming—the Upper Basin states—will have to reduce their usage, as well, though not by as much as those pulling water from the Lower Basin.