Albuquerque, N.M. – The U.S. Supreme Court on Monday sided with New Mexico in a fight with Texas over the Pecos River, issuing a decision that involves evaporation and New Mexico’s obligations to deliver water to its southern neighbor as part of a decades-old water-sharing compact.

The court decision found that the river master overseeing the compact correctly calculated that New Mexico should get credit for floodwater it stored in 2014. Even though it had requested that the water be stored upstream, Texas argued that a significant amount of water had evaporated while in storage and as a result New Mexico didn’t meet its obligations.

The dispute over how to account for the evaporated water ended up before the Supreme Court after Texas filed a motion seeking a review the river master’s decision.

In denying Texas’ motion, Justice Brett Kavanaugh wrote that the arguments presented by the Lone Star state disregarded the history of proceedings related to the Pecos River and that both states previously agreed to regulations that meant New Mexico would not be held accountable for evaporative losses.

Kavanaugh also noted that because of the irregular water levels on the Pecos, the compact does not require a specific amount of water to be guaranteed to Texas. Rather, the amount is based on the river’s present conditions.

New Mexico Attorney General Hector Balderas and the state’s top water official, State Engineer John D’Antonio, both said they were pleased with the court’s decision.

 D’Antonio said the state intended to continue meeting its obligations to Texas and had a strong credit under the compact.

New Mexico and Texas also are feuding over management of the Rio Grande – one of the region’s other major rivers – in a separate case pending before the Supreme Court. The outcomes of these interstate battles over water supplies are becoming even more important as New Mexico, West Texas and the rest of the American Southwest remain locked in drought.

In a nod to the region’s longstanding issues with water, the latest court decision offered some history about the Pecos River, saying the dry landscape has left farmers and ranchers in both states dependent on the waterway.

New Mexico ordinarily receives credit only for water that actually makes its way to Texas. There are exceptions, such as when water is stored upstream at Texas’s request. The court decision points to the river master’s manual, which spells out that New Mexico’s delivery obligation should be reduced by the amount of reservoir losses attributable to storage.

While the states negotiated for years over how to account for evaporation losses, talks eventually broke down as they were never able to reach an agreement.