Texas v. New Mexico

The Pecos River flows from New Mexico into Texas, and a 1949 interstate compact governs how much water New Mexico must allow to reach Texas each year. In 2014, a tropical storm threatened to flood Texas, so Texas's water official asked New Mexico to temporarily hold Texas's share of the river water in a New Mexico reservoir. New Mexico agreed but warned that evaporative losses would be Texas's responsibility. About 21,000 acre-feet of water evaporated before the stored water was released. Texas and New Mexico then disagreed sharply over who should bear that loss.

When Texas asked New Mexico to store Pecos River water to prevent flooding and some of it evaporated during storage, does New Mexico still get credit for that evaporated water under the two states' water-sharing agreement?

Yes — New Mexico is entitled to delivery credit for the water that evaporated. A 1988 court-adopted manual that implements the Pecos River Compact includes a provision (Section C.5) stating that when water from Texas's share is stored in a New Mexico facility "at the request of Texas," New Mexico's delivery obligation is reduced by any reservoir losses from that storage. Texas's own water commissioner sent New Mexico an email in November 2014 — with the subject line "Texas request for storage" — that squarely triggered this provision.

Texas's three counterarguments all failed. The stored water did qualify as the "Texas allocation" under the Compact, the water was plainly "stored" in the ordinary sense of the word, and Texas never rescinded its storage request or asked for release before August 2015 — so all the evaporation during that period counts against Texas. The timeliness objection also failed because both states had agreed to postpone the River Master's resolution of the dispute while they negotiated.

Water managers and officials in New Mexico, Texas, and other states sharing scarce river water now have clear guidance that when one state asks another to hold water and some evaporates, the requesting state absorbs those losses. This shapes how future emergency storage arrangements along the Pecos River — and potentially similar interstate compacts — will be negotiated and documented.

The River Master's determination stands, and New Mexico receives delivery credit for the approximately 21,000 acre-feet of water that evaporated during storage. Future water accounting under the Pecos River Compact will proceed under the same §C.5 framework the Court applied here. The Court left open a separate procedural question — flagged by Justice Alito — about whether the River Master had authority to amend the Manual's deadlines, which could arise in future disputes.

The Court did not decide whether the River Master's amendment to the Manual altering procedural deadlines was valid. Justice Alito argued the River Master lacks authority to change the amended decree's deadlines, but the majority declined to reach that question because it did not affect the outcome here.