This blog was guest authored by Tiffany Dowell Lashmet. Tiffany is an agricultural attorney with Texas A&M Agrilife Research and Extension Center out of Amarillo, TX where she authors the popular Texas Agricultural Law Blog.  Tiffany specializes in land use issues, estate planning and water law. She is a valued partner and friend of the National Agricultural Law Center.


The United States Supreme Court recently issued a unanimous opinion in an ongoing groundwater dispute between Mississippi and Tennessee. [Read Opinion here.]


Memphis sits in the southwest corner of Tennessee with Mississippi as its southern boundary.  Beneath Memphis sits the Middle Claiborne Aquifer (“the Aquifer”), which has provided Memphis with drinking water for well over 100 years.  The Aquifer underlies more than just Memphis, stretching beneath eight states in total, including Mississippi.

Wells extract water from the Aquifer.  These wells pump water to the surface, and in doing so, lowers water pressure around the well location. These areas are known as “cones of depression.”

The City of Memphis has more than 160 wells in and around the city pumping approximately 120 million gallons of groundwater each day from the Aquifer. Some are drilled near the Mississippi/Tennessee border, but none cross the state line. This pumping has caused a cone of depression underlying both Memphis and neighboring DeSoto County, Mississippi.

Prior Lawsuit

In 2005, Mississippi sued Memphis and its public water utility, Memphis Light, Gas & Water Utility alleging that Memphis’ pumping wrongfully appropriated groundwater belonging to Mississippi.  The trial court dismissed the case for failing to join Tennessee as an indispensable party and the United States Court of Appeals for the Fifth Circuit affirmed.

The US Court of Appeals for the Fifth Circuit held that interstate aquifers are similar to interstate rivers and, therefore, are subject to the doctrine of equitable apportionment.  This doctrine allows the United States Supreme Court to allocate rights in a disputed interstate water resource if one state sues another under the Court’s original jurisdiction.  Unless a statute, compact, or other apportionment controls, equitable apportionment has been the exclusive judicial remedy for these types of interstate water disputes.  Interestingly, the US Supreme Court had never decided whether an underground aquifer was subject to equitable apportionment.

Because the Fifth Circuit found that equitable apportionment was the proper method of determining the rights of the two states, the appellate court held that Tennessee was an indispensable party.  Mississippi could not add Tennessee to the lower court lawsuit because when a lawsuit is filed between states, the United States Supreme Court has exclusive jurisdiction.  This is known as “original jurisdiction” and is one of the rare cases where suits are filed in the US Supreme Court, rather than starting at a lower court and making their way there through the appellate process.

Mississippi sought a writ of certiorari from the United States Supreme Court, which was denied.  Its request for leave to file a complaint against Tennessee was also denied without comment.

Current Lawsuit

In 2014, Mississippi sought leave to file a complaint against Tennessee, the City of Memphis, and Memphis’ public utility in the United States Supreme Court. In its complaint, Mississippi claimed that Tennessee’s pumping of groundwater from the Middle Claiborne Aquifer resulted in the loss of hundreds of billions of gallons of groundwater that were once located under the state of Mississippi. In other words, Mississippi conceded that some water would naturally flow between states in the Aquifer but claimed that Memphis’ pumping has altered the historic flow of groundwater, allowing Memphis to take billions of gallons of groundwater that would otherwise remain under Mississippi. This, Mississippi argued, has resulted in Mississippi having to drill deeper wells to access the Aquifer and to use more electricity to pump the groundwater to the surface. Further, Mississippi argued absolute ownership of groundwater beneath its state, even after that water has crossed its border into another state. It claimed that Tennessee’s pumping is a tortious taking of property.

Importantly, Mississippi expressly stated that it was not seeking for the Court to apply equitable apportionment in this case, stating that the “fundamental premise of this Court’s equitable apportionment jurisprudence–that each of the opposing States has an equality of right to use the waters at issue–does not apply to this dispute.”

The complaint sought $615 million in damages as well as injunctive and declaratory relief. The Supreme Court granted Mississippi’s request to file the complaint and appointed a Special Master to manage the case.  (Commonly in suits of original jurisdiction, the Supreme Court will appoint a Special Master to oversee the case, including ruling on motions, conducting hearings, and even holding trials.  The Special Master will then offer the Court a recommendation of how to rule in the case, which the Court may adopt or reject.)

In November of 2020, the Special Master, Judge Eugene E. Siler, Jr., recommended that the Supreme Court dismiss Mississippi’s complaint with leave to amend.  [Read Report here.]   The Special Master found that the Aquifer is an interstate water resource, that it is a “single hydrogeological unit,” that Tennessee’s pumping affects groundwater beneath Mississippi, and that prior to this pumping, groundwater flowed between the two states.  Because he found the Aquifer an interstate water resource, he concluded that equitable apportionment was the only available remedy.  Because Mississippi’s complaint did not seek equitable apportionment, he recommended the Court dismiss the complaint, but grant Mississippi leave to file an amended complaint to seek equitable apportionment.

Both Mississippi and Tennessee filed exceptions to the Special Master’s report.  Mississippi objected to the recommendation that the Court dismiss the suit and claiming the Special Master erred in finding the Aquifer subject to equitable apportionment.  Tennessee objected only to the recommendation that the Court grant Mississippi leave to amend its complaint.

Supreme Court Opinion

Chief Justice Roberts authored the opinion of the court, which dismissed the case and declined to grant Mississippi leave to amend its complaint.

Applicability of Doctrine of Equitable Apportionment

The Chief Justice discussed the doctrine of equitable apportionment, and its guiding principle that States “have an equal right to make reasonable use of a shared water resource.”  He noted that the doctrine has been applied to interstate rivers and streams for decades.  It has also been applied to disputes over interstate river basins, such as the recent Florida v. Georgia decision from 2018, and to a case involving anadromous fish that travel down a river through several states.

The Court has not, however, considered whether equitable apportionment applies to interstate aquifers.  The Court turned its analysis to whether equitable apportionment of the Middle Claiborne Aquifer would be “sufficiently similar to past applications to warrant the same treatment.”  The Court found that it was sufficiently similar.

First, the Court easily determined that the Aquifer is, indeed, multi-state and a transboundary resource as it underlies multiple states.  Second, the Court noted that the water in the Aquifer flows naturally between states, just as does water (or fish) in all of its other equitable apportionment cases. The fact that the natural flow may be slow did not place the aquifer beyond the application of equitable apportionment, as Mississippi argued. Finally, the Court noted the interstate effects that Mississippi claims, including the cone of depression and reduced groundwater storage, are “a hallmark of our equitable apportionment cases.”   Based on this, the Court held the Aquifer is subject to the judicial remedy of equitable apportionment.

Mississippi next argued that because it has sovereign ownership of all groundwater beneath its surface, equitable apportionment does not apply.  The Court disagreed, as the Chief Justice wrote, “We see things differently.”

The Court agreed that each state has “full jurisdiction over the lands within its borders, including the beds of streams of and other waters.”  That does not, however, “confer unfettered ownership or control of the flowing interstate waters themselves.”  Although the Court’s past cases have involved streams and rivers, it saw no basis for a different result in the context of the Aquifer.  As the Court explained, when a water resource is shared between states, each has an interest that should be respected by the other.  Mississippi’s absolute ownership argument would allow an upstream state to completely cut off flow to a downstream state, which would be contrary to the equitable apportionment doctrine.

Mississippi relied upon the Court’s 2013 decision in Tarrant County Regional Water District v. Hermann to support its arguments.  The Court distinguished that case as it involved an interstate compact between Oklahoma and Texas.  Thus, the Court’s decision turned not on equitable apportionment, but the language of the compact.   The Court also noted that to the extent the Tarrant case stands for the proposition that one state may not enter another to take water absent an express agreement, that is not at issue in the instant case.  There is no allegation that Memphis has entered into Mississippi, as it is undisputed all wells at issue are drilled straight down in Tennessee and do not cross the state line.  The fact that the water–which is captured by Tennessee within its own bounds–may have originated in Mississippi may be relevant in considering equitable apportionment but is not mean the doctrine is inapplicable.

Because the Aquifer is subject to equitable apportionment, the Court overruled Mississippi’s exceptions and adopted the Special Master’s recommendation to dismiss the complaint.

Leave to Amend

The Special Master recommended the Court allow Mississippi to amend its complaint to seek equitable apportionment.  The Court held it need not decide this issue, because Mississippi did not seek leave to file such an amended complaint.  Nor, the Court noted, can it assume that Mississippi wants to do so, particularly because the initial complaint expressly disavowed the doctrine of equitable apportionment.  Instead, Mississippi brought tort claims.  An equitable apportionment cases would require a broader range of evidence and could require the joinder of additional parties, such as the other states under which the Aquifer lies. Additionally, an equitable apportionment case requires a state to prove real and substantial injury or damage by clear and convincing evidence.

Since Mississippi has not sought to amend, the Court saw no reason to determine whether such leave should be granted.   Thus, the case was dismissed without leave to amend.

Key Takeaways

The most important takeaway from this case is that the United States Supreme Court will apply the doctrine of equitable apportionment to interstate aquifers that meet three qualifications: (1) the aquifer is multistate; (2) the aquifer’s water flows naturally between the states; and (3) the actions of one state affects the portion of the aquifer below another state.

This issue had never been decided by the Court before and will now govern the rights of states when dealing with interstate aquifers.  States may now seek equitable apportionment of interstate aquifers from the Supreme Court assuming they can meet the legal requirements to do so.  Given the number of interstate water disputes around the country, this is an important decision and could impact future groundwater disputes between states.

Do keep in mind, however, that the application of equitable apportionment is limited and will not apply in situations where there may be a statute, compact, or other agreement between the states that dictates the share of water.  Some water lawyers have speculated that this ruling may prompt states to enter into compacts to address interstate aquifers now in order to provide certainty to states and not leave the apportionment in the hands of the Supreme Court.  That could be so, but don’t forget this would require the states to agree on a plan, and even if that happens, there are plenty of interstate water compacts that have also found their way to the Supreme Court in recent years.

It will be interesting to see how interstate groundwater law develops in the future in light of this decision.

Lastly, to hear more about this case and other water law cases at the United States Supreme Court, listen to this podcast episode with Jesse Richardson.