In an era when most Supreme Court opinions are sharply divided, last week the high court unanimously rejected Mississippi’s claim against Tennessee in a long-running dispute over the groundwater that lies beneath both states in a common aquifer.
The impacts of this case will extend far beyond Mississippi and Tennessee, as states compete with one another over limited water supplies.
When neighboring states fight over shared rivers, the law has been clear for more than a century: They can settle their differences either by negotiated agreements known as “interstate compacts” or they can ask the Supreme Court to divide up the waters through what is known as an “equitable apportionment.”
But until last week, it was not as clear how states should resolve brawls over water when it is found underground in geologic formations known as aquifers.
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Where the conflict began
Mississippi initiated the latest round of this confrontation in 2014 when it sued Tennessee for allegedly stealing hundreds of billions of gallons of groundwater that were once located beneath it.
Mississippi declined to pursue the traditional solutions of interstate compact or equitable apportionment, in part because it did not want to share what it viewed as “its” groundwater.
Instead, it claimed that it owned the water beneath its territory. Further, it claimed that Tennessee owed it at least $615 million for siphoning water from more than 160 wells in the Memphis area, some just a few miles from the state line.
Chief Justice Roberts quickly laid those claims to rest, explaining that Mississippi “contends that it has sovereign ownership of all groundwater beneath its surface, so equitable apportionment ought not apply. We see things differently.” This was the first time that the Court clearly held that equitable apportionment applies to interstate aquifers, just as it does to interstate rivers.
In a pointed rebuke, the court dismissed the complaint and declined to grant “leave to amend.” That means Mississippi will have to go back to the drawing board and specifically ask for an equitable apportionment if it wants to limit Tennessee’s pumping.
Among other things, Mississippi will have to show by clear and convincing evidence that Tennessee’s wells caused “substantial injury” to Mississippi. That is a stiff burden that many states have failed to sustain in past litigation over interstate rivers.
Why did it take so long for the Court to extend the equitable apportionment doctrine — which dates back to 1906 — to groundwater? Even before that doctrine was developed, mid-nineteenth-century judges viewed groundwater as so “secret” and “occult” that they deemed it impossible to regulate under the laws that applied to rivers.
It was not until the early 1900s that hydrologists had a firm understanding of the close interrelationship of surface and underground water, and not until 1937 that the invention of the high-speed centrifugal pump allowed us to extract significant volumes of groundwater.
But by then, the judicial aversion to groundwater regulation was firmly rooted and many water users had grown accustomed to circumventing laws applicable to surface water by instead pumping groundwater.
The law generally allowed them to do so, even if such wells withdrew water connected to protected surface streams. The law has been struggling to catch up with science ever since.
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What the Supreme Court ruled
In the short term, the Supreme Court has handed Tennessee a victory.
For now, the City of Memphis, through its public utility, can continue to pump some 120 million gallons of abundant, clean, affordable drinking water each day. But at some point, Mississippi or one of the other eight states that overlie the same aquifer might try again before the Supreme Court.
The court’s decree has broad ramifications long term.
First, it signals a victory for the integration of law and science. Beyond equitable apportionment, numerous other legal doctrines have treated groundwater as apart from the water cycle — something one could think of as “groundwater exceptionalism.”
The Mississippi v. Tennessee decision is an important judicial acknowledgement of the simple fact that surface water and groundwater are connected.
Second, groundwater disputes are becoming increasingly widespread. In the United States, there are 68 regionally extensive aquifers, with many of them crossing state boundaries. There should be no illusion that it will be easy to map complex aquifers and fairly divide up their water among competing states.
But as growth, drought and climate change exacerbate shortages, the states will need a clear legal roadmap for sharing scarce resources.
Fortunately, the Supreme Court has provided just such a guide in its recent decision
Christine A. Klein is the Cone, Wagner, Nugent, Hazouri & Roth Professor of Law at the University of Florida Levin College of Law.
This article originally appeared on Memphis Commercial Appeal: How the U.S. Supreme Court resolved Tennessee and Mississippi water dispute