Supreme Court Holds That Interstate Groundwater Can Be Subject To Equitable Apportionment
In Mississippi v. Tennessee, a potentially consequential case for groundwater rights in the Ogallala Aquifer, the court rejected Mississippi’s claim that Tennessee had stolen its groundwater.
The Supreme Court has issued an opinion in the long-running dispute over groundwater in the Middle Claiborne Aquifer. That aquifer underlies Mississippi, Tennessee, and five other states. Since 2005, Mississippi has maintained that Tennessee, and in particular the city of Memphis, has essentially stolen its groundwater. Specifically, Mississippi has claimed that by withdrawing water from the aquifer to supply its residents, Memphis has caused a zone of depression to form. This has pushed water from Mississippi’ side of the aquifer to Tennessee’s, allegedly invading Mississippi’s “sovereign” right to its water. Mississippi sought $615 million in damages as well as injunctive and declaratory relief. The Supreme Court accepted Mississippi’s petition for review in 2015.
In an article we recently published , we summarized this legal battle and predicted that the court would side with Tennessee. Indeed, in a unanimous opinion, the court rejected Mississippi’s claim. See Mississippi v. Tennessee, 595 U.S. __ (2021). The opinion is available here.
As we predicted, the court held that “equitable apportionment” was the only appropriate remedy. Under equitable apportionment, the court allocates rights to a disputed interstate water resource by principles of fairness. The doctrine’s “guiding principle,” according to the court, “is that states have an equal right to make a reasonable use’ of a shared water resource.” Equitable apportionment has served as the exclusive remedy for interstate surface-water disputes that lack a controlling statute, compact, or prior appropriation. But until this case, it was unclear whether the same doctrine would apply to interstate groundwater.
Resolving that question, the court found that the Middle Claiborne Aquifer was subject to equitable apportionment. Like interstate surface water, the aquifer:
- was of a “multistate character;”
- flowed naturally, albeit very slowly, between states; and
- was the object of one state’s “siphoning,” which reduced groundwater storage and pressure in another state.
Accordingly, because Mississippi had sued under only a tort theory of conversion and not under equitable appropriation, the court dismissed the suit.
The court’s decision is potentially consequential for water rights in Nebraska and surrounding states that overlie the Ogallala Aquifer. Although the court expressly limited its decision to the aquifer at hand, the opinion very likely means that the court would apply equitable apportionment in other interstate-groundwater disputes also. For instance, the Ogallala Aquifer underlies eight states (South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas). If one of these states grew dissatisfied by the others’ groundwater withdrawals, that dissatisfied state could seek equitable apportionment of the aquifer. The dissatisfied state would need to prove, by clear and convincing evidence, that the others’ Ogallala withdrawals have caused it a real and substantial injury or damage. See Florida v. Georgia, 141 S. Ct. 1175, 1180 (2021). If the court then granted review, it could impose significant limitations on groundwater withdrawals within those states.