Tex. Water Code § 26.023
The commission by rule shall set water quality standards for the water in the state and may amend the standards from time to time. The commission has the sole and exclusive authority to set water quality standards for all water in the state. The commission shall consider the existence and effects of nonpoint source pollution, toxic materials, and nutrient loading in developing water quality standards and related waste load models for water quality. The commission shall develop standards based on all quality assured data obtained by the commission, including the local watershed and river basin database described by Section 26.0135(c)(2). In this section, "quality assured data" has the meaning assigned by Section 26.0135(i).
Tex. Water Code § 26.023