Both are hot and dry, which many people love. Hot and dry > hot and humid, which is Texas, Florida, and most of the area in between. Nevada, Arizona, Texas, and Florida are the top retirement destinations for folks from the Midwest and Northeast, sick of cold and snow. Personally I prefer Las Vegas to the others because it's dry and doesn't have bugs (unlike Texas and Florida) but it's not quite as hot as Phoenix (which runs about 10'F hotter).
Water wise, Lake Mead is the largest reservoir in the United States, less than an hour's drive away from downtown Las Vegas. Lake Mead's water is used by several states under a complicated water sharing agreement, but push come to shove, you can't physically move it out of Nevada. No significant water use restrictions have been placed on Las Vegas. By contrast, look at the situation in California, where some towns have had to resort to trucking in water because even their groundwater resources are entirely depleted.