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Vol. 52-2 Water Rights

October 4, 2022

Water Rights

Mississippi v. Tennessee: A Watershed Decision in State Water Rights


            In Mississippi v. Tennessee,[1] the states of Mississippi and Tennessee disagreed about what rights each state had to the groundwater resources of the Middle Claiborne Aquifer. Mississippi filed an action against Tennessee and, in a novel argument, claimed that Tennessee’s pumping of the groundwater in the Aquifer amounted to a tortious taking of groundwater owned by Mississippi.[2] The United States Supreme Court held that Mississippi did not own the groundwater; rather, the Aquifer’s water resources were subject to equitable apportionment between the states.[3] 


The Middle Claiborne Aquifer is a large freshwater aquifer that underlies eight states, including Mississippi and Tennessee, both of which rely on this water resource daily.[4] Groundwater pumps draw water to the surface, where the water is transported to consumers.[5] The Aquifer is a main source of water for the City of Memphis which, through its utility, draws about 120 million gallons of water per day from Memphis’s more than 160 groundwater wells.[6] All of the wells are drilled straight down and located within Tennessee’s borders, but importantly, some are near the Tennessee-Mississippi border.[7]

Pumping groundwater creates a cone of depression that lowers water levels around the wells. This phenomenon can be controversial when the wells are close to state borders, because the wells—while themselves entirely within state borders—can lower water levels across state lines.[8] Here, Mississippi argued that the City of Memphis’s pumping activities “altered the historic flow of groundwater within the Middle Claiborne Aquifer.”[9] Specifically, Mississippi alleged that Memphis’s groundwater pumping substantially lowered water pressure and decreased groundwater drawdown in the parts of the Aquifer located in Mississippi near the Mississippi-Tennessee border.[10] Mississippi did acknowledge that 30–60 feet of water per year flowed naturally through the Aquifer from Mississippi to Tennessee, but Mississippi contended that Memphis’s pumping “substantially hastened this existing flow.”[11] As a result of the pumping in Tennessee, Mississippi asserted that it was forced to drill deeper wells “and use more electricity to pump water to the surface.”[12]

Rather than filing an original action seeking equitable apportionment—the usual judicial remedy for the apportionment of the shared water resource—Mississippi claimed that the doctrine did not apply because it had a sovereign ownership right to the groundwater beneath its borders.[13] Mississippi therefore sought leave to bring an original action against Tennessee on the basis that Memphis tortiously took “hundreds of billions of gallons of high-quality groundwater owned by Mississippi.”[14] Mississippi sought $615 million in damages.[15] Mississippi also contended that equitable apportionment does not apply to groundwater use.[16] 

Legal Background and Question

            Equitable apportionment is a judicial remedy that seeks to fairly allocate a shared water resource between two or more states, based on the idea that states have an equal right to reasonable use of shared water resources.[17] The United States Supreme Court has applied equitable apportionment to interstate rivers, streams, river basins, and in situations where groundwater pumping has affected the flow of interstate surface waters.[18] Since the Court had never answered the question of whether equitable apportionment applies to interstate aquifers, this case was a matter of first impression.[19] The question in this case, then, was whether equitable apportionment of an interstate aquifer is “‘sufficiently similar’ to past applications of the doctrine to warrant” the application of equitable apportionment.[20]

The Court’s Analysis

            The Court unanimously held that equitable apportionment of the Aquifer was sufficiently similar to past applications such that it warranted application in this case.[21] The Court asserted three primary reasons for its holding.

First, the Court noted that the Aquifer is multistate in character.[22] The Court had only applied equitable apportionment in the past to interstate water resources, and this case unquestionably involved an interstate water resource.[23] Mississippi did not contest the scientific consensus that the “‘Aquifer is a single hydrogeological unit’ spanning multiple states.”[24] 

Second, the Court observed that the groundwater in the aquifer “flows naturally between the states.”[25] This again rendered the aquifer similar to the Court’s past applications of equitable apportionment, which all involved water that flowed naturally across state boundaries.[26] Mississippi argued that the aquifer’s water flow was distinguishable from that of the past applications of equitable apportionment because the aquifer flows “extremely slow[ly].”[27] The Court remained unpersuaded, observing that it had applied equitable apportionment to water resources that sometimes run dry.[28] The Court also stressed that while the speed of the water’s flow may be slow, the volume of the water flowing totaled more than “35 million gallons of water per day, and over ten billion gallons per year.”[29] Thus, the speed at which the aquifer flows failed to distinguish the aquifer from the water resources to which the Court normally applied equitable apportionment.[30]

Lastly, the Court pointed out that the City of Memphis’s pumping activities affected the aquifer underneath Mississippi.[31] Pumping water from the aquifer within Tennessee’s borders reduces groundwater pressure and drawdown miles into Mississippi.[32] “Such interstate effects are a hallmark of [the Court’s] equitable apportionment cases.”[33] For the three reasons stated above, the Court held that the groundwater in the aquifer is subject to equitable apportionment.[34]

Mississippi insisted that it holds “sovereign ownership of all groundwater beneath its surface, so equitable apportionment ought not apply.”[35] The Court disagreed, explaining that while states own the land and waterbeds within their borders, this ownership does not extend to the “flowing interstate waters themselves.”[36] The Court also commented that if states could exercise jurisdiction over all of the groundwater underneath the state, then upstream states could pump aquifers dry and leave downstream states without water.[37]

Mississippi also urged that Tarrant Regional Water District v. Herrmann supported Mississippi’s argument that equitable apportionment should not apply.[38] In Tarrant, the Supreme Court interpreted a compact that two states had negotiated concerning the states’ rights to a water resource.[39] The Tarrant Court did not consider whether equitable apportionment applied in that case, because the dispute was solely governed by the contract.[40] Accordingly, the Court explained that Tarrant was inapposite.[41]

The Court recognized that Tarrant did support the rule that states “may not physically enter another to take water in the absence of an express agreement,” but that was not at issue here—the City of Memphis’s wells were undisputedly within Tennessee’s borders.[42] That some of the aquifer’s water began in Mississippi did not affect the analysis; just as river water may originate in another state, so too may groundwater.[43] While “[t]he origin of an interstate water resource may be relevant to the terms of an equitable apportionment . . . . that feature alone cannot place the resource outside the doctrine itself.”[44] Since Mississippi and Tennessee did not have a contractual agreement about their respective rights to the groundwater, and Tennessee was pumping water in its own state, no rule in Tarrant supported Mississippi’s argument that equitable apportionment should not apply.[45] 

In sum, the Court held that the groundwater in the Middle Claiborne Aquifer was subject to equitable apportionment because it the aquifer was sufficiently similar to the water resources that are customarily subject to equitable apportionment. The Court dismissed Mississippi’s complaint.[46]

Implications for State Water Rights

            As climate change prompts governments to pay closer attention to the use and conservation of water resources, this decision has important ramifications for state water rights. This case appears to stop states from attempting to pump important groundwater resources dry: If Mississippi were able to assert ownership over all of the groundwater within its state borders, then it is in Mississippi’s interest to use as much of that groundwater as possible, lest Tennessee endeavor to do the same. This, of course, would not be a conservation-conscious practice. Equitable apportionment aspires to ensure that states fairly share and preserve water resources. But as the Court noted in this case, states seeking judicial enforcement of equitable apportionment must show real and substantial injury, which is a high bar.[47]

            This ruling also may inspire states to adopt interstate compacts concerning groundwater resources. Because of the cost and difficulties involved in obtaining judicial enforcement of equitable apportionment, a proactive compact is an attractive option for states looking to secure long-term rights to interstate groundwater resources. Predictable judicial enforcement makes compacts reliable and financially prudent. Indeed, the Court in this case explicitly distinguished Tarrant on the grounds that Tarrant was a question of contractual interpretation.[48] The market forces underlying the negotiations of such compacts also give assurance that groundwater resources will be used efficiently by the states that are parties to the compact.


Graham Rex is a rising 3L from Raleigh, North Carolina. He studied Philosophy at the University of North Carolina-Wilmington, and he joined TELJ during his 1L year. Graham wants to practice nonprofit environmental law after law school and he is clerking at Earthjustice in Denver, Colorado this summer. 


Emily Rogers is the Managing Partner of Bickerstaff Heath Delgado Acosta LLP and represents public and private clients in water rights, water quality, utility, and environmental law matters.


Kimberly Kelley is an attorney at Bickerstaff Heath Delgado Acosta LLP and practices in the areas of municipal, open government, water, and environmental law. She earned her undergraduate degree from Texas A&M University and graduated Texas Tech University School of Law, where she served on the editorial board of the Law Review.




[1] Mississippi v. Tennessee, 142 S. Ct. 31 (2021).

[2] Id. at 38.

[3] Id. at 41.

[4] Id. at 36.

[5] Id.

[6] Id. at 37.

[7] Id.

[8] Id.

[9] Id.

[10] Id. at 38.

[11] Id. at 37.

[12] Id. (citing Complaint at ¶ 54(b), Mississippi v. Tennessee, 142 S. Ct. 31 (2021)).

[13] Id. at 40. 

[14] Id. at 38 (quoting Complaint at ¶ 23, Mississippi v. Tennessee, 142 S. Ct. 31 (2021)).

[15] Id. (citing Complaint at ¶¶ 55–56, Mississippi v. Tennessee, 142 S. Ct. 31 (2021)).

[16] Id. (citing Complaint at ¶ 49, Mississippi v. Tennessee, 142 S. Ct. 31 (2021)). Equitable apportionment seeks to divide rights to an interstate water resource fairly between states. The doctrine will be discussed in detail later in this essay.

[17] Id. at 39 (citing Colorado v. New Mexico, 459 U.S. 176, 183 (1982); Florida v. Georgia 141 S. Ct. 1175, 1180 (2021)).

[18] Id.

[19] Id.

[20] Id.

[21] Id.

[22] Id. at 39–40.

[23] Id.

[24] Id. at 40 (citing Report of Special Master at 20, Mississippi v. Tennessee, 142 S. Ct. 31 (2021)).

[25] Id.

[26] Id.

[27] Id. (quoting Exceptions Brief for Mississippi at 8, Mississippi v. Tennessee, 142 S. Ct. 31 (2021)).

[28] Id. (citing Kansas v. Colorado, 206 U.S. 46, 115 (1907)).

[29] Id. (citing Hearing Tr. 532–33, Mississippi v. Tennessee, 142 S. Ct. 31 (2021)).

[30] See id.

[31] Id.

[32] Id.

[33] Id. (citing Florida v. Georgia 141 S. Ct. 1175, 1180 (2021)).

[34] Id.

[35] Id.

[36] Id. (citing Wyoming v. Colorado, 259 U.S. 419, 464 (1922)).

[37] Id. at 41.

[38] Mississippi v. Tennessee, 142 S. Ct. at 41 (citing Tarrant Reg’l Water Dist. v. Herrmann, 569 U.S. 614 (2013).

[39] Id. (citing Tarrant, 569 U.S. at 627).

[40] Id. 

[41] Id.

[42] Id. (citing Joint Statement of Stipulated and Contested Facts at 106, Mississippi v. Tennessee, 142 S. Ct. 31 (2021)).

[43] Id. (citing Colorado v. New Mexico, 459 U.S. 176, 181, n.8 (1982); Idaho ex rel. Evans, 462 U.S. 1017, 1028, n.12 (1983)).

[44] Id.

[45] Id.

[46] The Court declined to decide whether Mississippi should be granted leave to file an amended complaint seeking equitable apportionment, because Mississippi never sought equitable apportionment. Id. Since Mississippi expressly rejected equitable apportionment in its pleadings, the Court could not assume that Mississippi would seek equitable apportionment. Id. (citing Complaint at ¶ 38, Mississippi v. Tennessee, 142 S. Ct. 31 (2021)). An equitable apportionment case would require consideration of more evidence, perhaps including “existing uses, the availability of alternatives, practical effects, and the costs and benefits to the states involved.” Id. An equitable apportionment claim might also require other parties to be joined, since other states also depend on the Aquifer’s water resources. Id. at 42. Lastly, a state pursuing equitable apportionment must prove a real and substantial injury. Id.

[47] See Mississippi v. Tennessee, 142 S. Ct. at 42 (citing Idaho ex rel. Evans, 462 U.S. 1017, 1028, n.12 (1983)).

[48] See id. at 41.