N.M. Stat. § 72-3-1
The state engineer shall, from time to time, as may be necessary for the economical and satisfactory apportionment of water, divide the state in conformity with the drainage areas into water districts to be designated by names, and to comprise as far as possible one or more distinct stream systems in each district. Districts may be changed from time to time as may, in his opinion, be necessary for the economical and satisfactory apportionment of water. Provided, that the state engineer may, when in his opinion it shall be for the best interests of the state and the owners of water rights upon any stream system within the state of New Mexico, divide said stream system into subdistricts, each of which said subdistricts shall be designated by a distinct name.
NMS § 72-3-1