Co-authored by Wes Miliband and guest-blogger Hayley K. Siltanen

The Ninth Circuit recently ruled that federal reserved water rights held by Indian tribes extend to groundwater underlying reservation lands. Determining the quantity of that groundwater, however, is reserved for another day.

In Aqua Caliente Band of Cahuilla Indians v. Coachella Valley Water District, the Ninth Circuit affirmed the district court’s declaration that the United States impliedly reserved appurtenant water sources, with “appurtenant” including groundwater, when it created the Aqua Caliente Band of Cahuilla Indians’ reservation in the Coachella Valley of California. The decision marks the first time that a federal appellate court has recognized groundwater rights as being included in federal reserved water rights.

Federal reserved rights are water rights that are appurtenant to land that has been withdrawn from the public domain by the federal government, and that are necessary to accomplish the federal purpose of the withdrawn (or “reserved”) land. In a landmark decision issued over 100 years ago, Winters v. United States, the U.S. Supreme Court held that federal reserved rights apply to Indian reservations. These rights, known as Winters rights, derive from the federal purpose of the reservation.  In the case of the Aqua Caliente Band of Cahuilla Indians (the “Tribe”), the Ninth Circuit explained that, “[w]ithout water, the underlying purpose—to establish a home and support an agrarian society—would be entirely defeated.”

After examining the realities of water supplies in the arid West—where groundwater is often the only viable water source—the Ninth Circuit found “no reason” to limit Winters rights to surface water rights. Although the recognition that federal reserved rights include groundwater is a significant development in tribal water right law (and for other federal interests with a federal reserved right such as with a military installation), much more hard work lies ahead.

The litigants will now seek to determine the quantity of the groundwater rights held by the Tribe.  That quantity may turn on how a court characterizes the federal purpose of the reservation.  What the quantity will not depend on, however, is state water rights law.  The Ninth Circuit stated explicitly that “state water rights are preempted by federal reserved rights.”  The court also made clear that federal reserved rights cannot be lost through non-use and do not depend on the water presently needed to sustain the reservation.  The parties will rely on these guidelines when moving forward to determine the quantity of the groundwater rights held by the tribe.

Ultimately, this decision speaks to the complexities of water rights law and related issues involving water quality and state water rights law.

A copy of the decision is available at: