Typically in cases where states have a dispute over water use, usually involving water flowing above ground in a river or lake, the Court uses the doctrine of equitable apportionment to allocate the water resources between the states. In Mississippi v. Tennessee, Mississippi originally sued the City of Memphis for drawing too much water from the Middle Claiborne Aquifer, which resides beneath both Mississippi and Tennessee, and asked for damages in federal court. The district court and the Fifth Circuit both held that since water flowed over state lines underground in the aquifer, like an aboveground river, then the case was really a water use dispute between the states subject to the equitable apportionment doctrine, and not damages. Mississippi re-filed its suit, adding Tennessee as a defendant, and again asked for damages instead of equitable apportionment, arguing that underground interstate aquifers should not be subject to the doctrine. The Court, in a unanimous ruling by Chief Justice Roberts, disagreed, holding that underground interstate aquifers should be treated as interstate rivers, especially where, as here, the water in the aquifer flows from one state to another. While Mississippi undoubtedly has sovereign ownership of the water within its boundaries, it has no such ownership over waters that pass over its boundaries that would afford it a claim for damages. Since Mississippi did not seek equitable apportionment, as would be the only available remedy, the case was dismissed. A link to the decision is here: https://www.supremecourt.gov/opinions/21pdf/143orig_1qm1.pdf