Most Native American tribes have at least some land that was reserved by the federal government for the purpose of creating a homeland for the Tribe. Under the Wintersdoctrine, established by the United States Supreme Court in 1908,1 the reservation generally includes some amount of water necessary to support the purposes of the homeland. This doctrine provides that when the United States "withdraws its land from the public domain and reserves it for a federal purpose, the Government, by implication, reserves appurtenant water then unappropriated to the extent needed to accomplish the purpose of the reservation."2 Such rights "vest[] on the date of the reservation and [are] superior to the rights of future appropriators," and arise and are determined under federal law.3

The majority of courts to have considered the issue have concluded, that with regard to Indian water rights claims, Winters rights include groundwater rights.4 In one case, however, the Supreme Court of Wyoming concluded that Winters rights did not include groundwater rights because the reservation did not explicitly include groundwater.5 In the most recent case to consider the question, Agua Caliente Band of Cahuilla Indians v. Coachella Valley Water District,the court ruled "[a]ppurtenance, as that term is used by the Winters doctrine, must provide some legal limitation to impliedly reserved water rights; but persuasive authority suggests that limit should not be drawn between surface and groundwater sources."6 Rejecting the Wyoming Supreme Court's ruling, Agua Caliente noted that since 1988, "[t]he weight of authority on the issue has shifted"7 —and it cannot seriously be questioned that reserved water rights include groundwater rights. (The district court, however, did reject the Agua Caliente Band's argument that they had an aboriginal right to groundwater on statute of limitations grounds.)

The Coachella Valley Water District and the Desert Water Agency have petitioned the Ninth Circuit Court of Appeals to appeal the question of whether the Tribe has a federal reserved right to groundwater. The Tribe and the United States opposed the petition.