This probably won't surprise you: Arizona is hot and dry. In fact, much of Arizona is coping with the 11th straight year of drought.
This won't surprise you either: what's commonsense here at home isn't always so in Washington. In the early days of the Clean Water Act, the federal government largely had authority over real sources of permanent water. But the Army Corps of Engineers now regulates not-so-wet-things like road-side ditches and sandy desert bottoms that might contain water once a year, if ever.
Expanding federal power can't be squared with state sovereignty or individual property rights. Private property rights are infringed when landowners are told they can't build because their dry land might be wet someday.
The old cowboy saying "it doesn't take a genius to spot a goat in a flock of sheep" seems fitting here. Just the same, it doesn't take a genius to know what's wet in Arizona. Environmental protection is done best when it's done close to home; locals know how to protect both their natural resources and private property rights.
-Competitive Enterprise Institute: "Supreme Court Reviews Water Quality Regulations"
-Goldwater Institute: "When a Puddle is Just a Puddle"
-Arizona Department of Water Resources: Drought Monitor Reports
-U.S. Senate Committee on Environment & Public Works: Hearing Statements on "Waters of the United States"