Coverage-Aware Break-Even Conditions for Polymeric Membrane-Based Water Reuse in Arid Urban Systems

A utility reclaiming effluent with polymeric membranes must choose a configuration and a deployment coverage. A coverage-aware volume and cost model for an illustrative arid zone of $10{\mathrm{Mm}}^3$/yr compares ultrafiltration (Configuration A) with ultrafiltration plus polyamide thin-film-composite reverse osmosis (Configuration B). Membrane parameters are literature-derived, eligibility and placement assumed, and no experiments were performed. At 50% coverage and 1 USD/m${}^3$, Configuration A avoids 11.5 percentage points of potable input at 0.48 USD/m${}^3$ and Configuration B 20.4 points at 0.70 USD/m${}^3$, or 0.56 and 0.82 USD/m${}^3$ without real-loss credit. Break-even coverages are 11.7% and 11.5%. Configuration B is preferable above a crossover value of 0.98 USD/m${}^3$ (1.15 without loss credit) and leads in 46.2% of paired draws at 1 USD/m${}^3$. Feed salinity, regulation, concentrate cost, and capital and financing costs move the crossover most. Under independent inputs and assumed eligibility, approved demand rather than recovery limits volume in at least 98.8% of draws, and placement dominates net-benefit variance. Adverse feed conditions that couple operating and cost parameters make treatment costs comparably influential for Configuration B. The thresholds are conditional criteria, not city-specific predictions.