The Southern Nevada Water Authority has banned evaporative cooling in new commercial buildings because the systems are one of largest consumers of water in Clark County. The ban went into effect this month but does not apply to businesses that applied for building permits before then. … Evaporative cooling is the second-largest consumptive use of water in Southern Nevada, behind outdoor irrigation. It uses about 10 percent of the region’s annual allotment of water from the drought-stricken Colorado River. Conserving water is paramount in Nevada as officials continue to address the challenges of a hotter, drier climate and overuse of the river.