30 Tex. Admin. Code § 298.20
An environmental flow standard or set-aside established under this chapter for a river basin and bay system other than the middle and lower Rio Grande shall be assigned a priority date corresponding to the date the commission receives environmental flow regime recommendations from the applicable basin and bay expert science team as set forth in these rules. This priority date shall be included in the appropriate water availability models maintained by the commission in connection with an application for a permit for a new appropriation or for an amendment to an existing water right that increases the amount of water authorized to be stored, taken, or diverted. The priority date for the environmental flow standards will be used in the water availability determination for a new appropriation or for an amendment to an existing water right that increases the amount of water authorized to be stored, taken, or diverted and has no other purpose.
30 Tex. Admin. Code § 298.20