This past fall, federal courts put a temporary halt on the Environmental Protection Agency's attempt to redefine "waters of the United States." The well-known rule would expand EPA power over nearly every wet patch in America, including puddles. But this is not the only important case in the courts today about federal control of water.

Back in 2009, when the new Waters of the United States rule was still just some bureaucrat's bad idea, the EPA began a separate power grab. And the Supreme Court may soon choose to review it.

Near the beginning of his first term, President Obama issued an executive order on "Chesapeake Bay Protection and Restoration." It called on EPA to develop a plan that would impose new responsibilities to limit each source of pollution within the bay's watershed, which extends as far west as West Virginia and as far north as central New York state.

In 2010, EPA released a 280-page document which went well beyond its statutory mandate. Whereas the Clean Water Act calls for the agency to set limits on the "Total Maximum Daily Load" of pollutants (in this case nitrogen, phosphorous and other nutrients), the EPA subdivided the watershed into 92 separate segments and set thousands of separate limits for the smaller units within them. This allows EPA to impose sanctions and forbid various economic activities within the watershed even if the total amount of pollution running off into the bay is below the overall limit.

The American Farm Bureau Federation filed suit in 2011, arguing that the EPA was claiming extensive powers over local land use that it was never meant to have. The bureau's petition notes, "As a practical matter, the power to set numeric limits for sediment and nutrients by source type within specific geographic areas equals nothing short of the power to allow farming here, but not there, building here, but not there."

State and local governments, who traditionally make land use decisions and with whom EPA is legally obliged to cooperate, say EPA's goals are unattainable. Pennsylvania's Department of Environmental Protection has called EPA's calculation of local limits "wholly unjustified and arbitrary and capricious."

The EPA's plan, like so much that it does, is both economically damaging and anti-constitutional in its distribution of powers. It would have the federal government taking on zoning powers reserved to states, counties and towns. Federal sanctions could be imposed and federal permits required for several activities that have not previously been considered "point sources" of pollution.

Importantly, this policy would doubtless leak out from the Chesapeake watershed and across the rest of America. It is, the Farm Bureau argues, a blueprint for future regulation of all other watersheds. The EPA could literally become a national zoning board.

So far, the Obama administration has been winning this legal battle to arrogate powers to the EPA. It won the case in federal district court, and again in the Third Circuit Court of Appeals. But these rulings seem to contradict recent Supreme Court rulings that set limits on how far federal agencies can go in rewriting statutes.

Everyone wants clean water, and efforts to date have already brought dramatic improvement to the long-ailing Chesapeake. According to the EPA, nitrogen and phosphorus emissions are down 21 percent since 1985, and sediment pollution is down 30 percent. The bay's water quality has improved gradually since then, as one would hope.

But whatever the outcome, processes matter, too. Government processes can either safeguard personal and economic freedoms, or they can erode them.

Neither Obama's nor any other president's EPA should have the sweeping powers over all economic activity that it is claiming with this watershed plan. Nor can the constitutional order bear them.