By The Arizona Republic Editorial Board 

A proposed EPA rule could have profound negative impacts on Arizona and its water supply.

The problem is as close as your kitchen sink.

Alarm bells are being sounded by Sens. Jeff Flake and John McCain, the Arizona Farm Bureau, water lawyers, ranchers and the head of Central Arizona Project.

The Environmental Protection Agency says it is only attempting to clarify the definition of "waters of the United States" in the Clean Water Act. This is needed because U.S. Supreme Court cases in 2001 and 2006 left too many uncertainties, the EPA says.

But the best intentions can’t prevent unintended consequences from zapping Arizona.

Consider: The CAP Canal currently enjoys an exemption written specifically for Arizona and other states with similar water systems. But the exemption is under court challenge that could leave the canal fully subject to the proposed rule, which "clearly encompasses us," says David Modeer, general manager of the CAP.

The EPA says it would not impose the rule on the CAP. But if the rule does not specifically exclude the canal system, a third party could go to court to demand compliance.

If that happened, the CAP could be required to get a permit before doing any maintenance work on the system, an expensive and time-consuming process that could delay delivery of water to Arizona’s major metropolitan areas, Modeer says.

What’s more, the CAP could be required to treat water in the canal when it enters and leaves Lake Pleasant, where large amounts of CAP water are stored for later delivery.

That’s ridiculous. CAP water has to meet Safe Drinking Water Act standards before it is delivered to homes, so adding this requirement would be redundant, pointless and enormously expensive — if it were even technically possible to do in a timely manner on such a massive scale.

Agricultural interests in Arizona also express concerns about what is being characterized as a jurisdictional land grab by the EPA.

In a recent op-ed, rancher and Arizona Farm Bureau First Vice President Stefanie Smallhouse wrote that "every dry wash in Arizona would now be considered ‘connected’ to a navigable waterway and subject to a permit."

In a letter to the EPA, McCain and Flake echo these concerns that "every small ephemeral system … would be regulated."

Jared Blumenthal, EPA administrator for Region 9, which includes Arizona, said, "We are not expanding jurisdiction." He added that nearly five dozen exemptions in the rule apply to agricultural activities.

Yet Arizona’s agricultural interests — farmers and ranchers — read the proposal and worry that routine activities would be subject to burdensome new regulations.

Environmental-law attorney Michelle De Blasi said if the EPA is not expanding jurisdiction, it needs to specifically state that in the final rule. The proposed rule is open to interpretation and court challenges.

Blumenthal said the EPA will consider everything submitted during the public-comment period, which runs through July 21. "We want to get this right," he said.

Getting it right means taking into account the needs of this arid state.

The Clean Water Act is an important piece of environmental law, but rules aimed at protecting the nation’s waterways should not inadvertently create havoc in Arizona.