40 CFR § 142.72 - Requirements for Tribal eligibility.
The Administrator is authorized to treat an Indian tribe as eligible to apply for primary enforcement for the Public Water System Program and the authority to waive the mailing requirements of § 141.155(a) if it meets the following criteria:
(a) The Indian Tribe is recognized by the Secretary of the Interior.
(b) The Indian Tribe has a tribal governing body which is currently “carrying out substantial governmental duties and powers” over a defined area, (i.e., is currently performing governmental functions to promote the health, safety, and welfare of the affected population within a defined geographic area).
(c) The Indian Tribe demonstrates that the functions to be performed in regulating the public water systems that the applicant intends to regulate are within the area of the Indian Tribal government's jurisdiction.
(d) The Indian Tribe is reasonably expected to be capable, in the Administrator's judgment, of administering (in a manner consistent with the terms and purposes of the Act and all applicable regulations) an effective Public Water System program.