Tex. Water Code § 49.509

(a) Subject to Subsection (d), the Rio Grande Regional Water Authority annually at its January meeting shall calculate the current market value by using the average price per acre-foot of municipal use water after conversion from irrigation use water to municipal use water with a municipal priority of allocation under commission rules of the last three purchases involving:

(1) a municipal water supplier;

(2) a party other than a municipal water supplier; and

(3) at least 100 acre-feet of municipal use water, with municipal priority of allocation.

(b) The Rio Grande Regional Water Authority shall use information from the water rights sales contracts reported to the Rio Grande Watermaster's Office to calculate the current market value.

(c) The Rio Grande Regional Water Authority shall make the calculation:

(1) without charging any of the parties involved; and

(2) using 100 percent of the value of monetary exchanges, not in-kind exchanges.

(d) For purposes of this subsection, "outer boundaries of a district" means a district's boundaries without considering any exclusion of land from inside the district. The Rio Grande Regional Water Authority shall exclude from the calculation of current market value under Subsection (a) any sale between a municipal water supplier and a district if any territory inside the outer boundaries of the district is:

(1) subject to the municipal water supplier's certificate of convenience and necessity; or

(2) in the corporate limits of the municipality served by the municipal water supplier, if the municipal water supplier does not hold a certificate of convenience and necessity.