...S&P Global Ratings assigned its '###' rating to the Trinity River Authority (TRA), Texas' Mountain Creek regional wastewater system's 2018 revenue bonds. The rating reflects the credit quality of the system's customer cities, specifically Grand Prairie, which we view as the strong link among the participants in the TRA system despite its position as the smallest participant. We have also affirmed our '###' rating on the system's parity debt. The outlook is stable. Payments are based on the participants' sewer flows as a percentage of total flows to the plant, although Grand Prairie also has a contractual minimum annual obligation. The contracts require unconditional payment by the participants to TRA. While there is no explicit language requiring a reallocation of expenses should a participant fail to pay, the authority can recalculate participant obligations at any time under a broad range of circumstances, effectively providing a step-up provision. The rating also reflects our opinion...