The Winters doctrine, derived from a 1908 US Supreme Court case, is commonly viewed as the basis for establishing federal reserved water rights for Indian Tribes. It has traditionally been construed to apply to Indian claims to surface water rights. The extent and scope of Indian water rights has been much litigated in the years since Winters v. United States was decided more than 100 years ago. A recent lawsuit by the Agua Caliente Band of Cahuilla Indians sought to test the boundaries of the Winters implied water rights doctrine by taking it in an entirely new direction—the Agua Caliente Band, with the backing of the United States federal government, asserted that its water rights could extend to groundwater.

A new decision by the Ninth Circuit Court of Appeals has put a limit on any tribal water rights claims to groundwater. In Agua Caliente Band of Cahuilla Indians v. Coachella Valley Water District, decided March 7, 2017 (available here), the Ninth Circuit held that the tribe could assert a reserved water right only "to groundwater underlying its reservation." In doing so, the Ninth Circuit affirmed the limited nature of Winters rights, saying "the Winters doctrine only applies in certain situations: it only reserves water to the extent it is necessary to accomplish the purpose of the reservation, and it only reserves water if it is appurtenant to the withdrawn land." The court explained that "appurtenant" means "waters which are attached to the reservation."

In the area of California where the Agua Caliente Band resides, "surface water is virtually nonexistent in the valley for the majority of the year" and "almost all of the water consumed in the region comes from the aquifer underlying the valley." In this context, the Ninth Circuit was "concerned on appeal only with...whether the Tribe has a federal reserved right to groundwater underlying its reservation," and concluded that it could assert such a right. In recognizing limits on the extension of Winters rights to groundwater, the court was careful to apply its ruling to groundwater underlying the reservation only. Therefore, Agua Caliente does not stand for the proposition that a tribe may assert implied reserved rights to groundwater far from reservation lands. In fact, the Ninth Circuit seems to have shut the door to any such notion by emphasizing that Winters rights, even if applicable to groundwater in some situations, must be limited to water attached to and underlying reservation lands.

In its recent decision, the Ninth Circuit provided important clarification on the limited scope of Winters rights available to tribes within its jurisdiction of Western states. It remains to be seen whether other federal circuits or the U.S. Supreme Court will agree.