Hispanic communal irrigation practices originated from Spanish colonization practices and laws. Disputes continue about the exact nature of this Spanish heritage because New Mexico towns claim that Pueblo rights are superior to subsequent Anglo appropriations. But these arguments aside, the basic thrust of Spanish water policy, as set forth in the late eighteenth century Plan de Pitic, was that available water supplies were to be shared among colonists and Indians. In practice, Indian entitlements were limited, but they have always been a legitimate part of New Mexico's water system (Meyer, 1984).

Under Spanish law the right to use water for domestic uses followed from the grant of crown lands. Irrigation was a different matter: the crown reserved the right to grant or withhold irrigation rights with individual land grants because large-scale consumptive water use was a matter of community interest. In New Mexico, water rights could be obtained through an original land grant, through a subsequent administrative grant, or by a later judicial determination. This process, known as composition, could “cleanse, authenticate, and even alter original grants” and could resolve disputes through the application of equitable principles (Meyer, 1984). Voluntary use agreements also were recognized.

Spanish jurisprudence recognized a number of relevant principles that can be found to varying degrees in modern water law. Such factors include title based on a land grant, prior use, need, the protection of third parties, the relationship between the proposed use and the community interest, and legal right and whether the use was by a public community or private individuals. Prior use was important but not controlling. Third parties, which often meant Indians, were protected under Spanish jurisprudence, and third party interests included the crown or state interest (Meyer, 1984).

The Rio Grande is divided by the Rio Grande Compact of 1938 into two areas below and above Elephant Butte. Transfers can take place relatively freely within each area, but transfers between the two areas are difficult because they would upset the compact balance. The compact allocates the river among three states and between Mexico and the United States. Colorado and New Mexico have rights reflecting their historic uses above Elephant Butte Reser-