30 Tex. Admin. Code § 319.26
The commission may require more stringent quality levels than those specified in § 319.22 of this title (relating to Quality Levels-Inland Waters) and § 319.23 of this title (relating to Quality Levels-Tidal Waters) where necessary to insure protection of water in the state. The commission may authorize less stringent quality levels than those set forth in § 319.22 of this title (relating to Quality Levels-Inland Waters) and § 319.23 of this title (relating to Quality Levels-Tidal Waters) only where the applicant demonstrates that there will be no significant adverse impact on water quality and that the less stringent quality levels are necessary based on considerations consistent with the provisions of the Texas Water Code.
30 Tex. Admin. Code § 319.26