Hidden Desalination Commitment: Detecting Future Replacement Dependence Before Present Water Failure

A water system can meet every present potable-water requirement and still have crossed into a future in which replacement supply can no longer be avoided. This study formalizes that possibility as hidden desalination commitment (HDC): zero present desalination requirement together with positive minimum future replacement burden over a stated planning horizon and admissible policy set. We develop a location-neutral computational framework linking present adequacy, future burden, policy feasibility, groundwater salinity dynamics, uncertainty, and falsification. In a controlled nonlinear benchmark, HDC coexists with intervention leverage, but a physically motivated two-dimensional groundwater-salinity model rejects the stronger preservation-amplification hypothesis: across 64 parameter combinations, HDC occurs in all cases, whereas positive preservation amplification occurs in none; a 40-sample uncertainty experiment detects HDC in 97.5% of cases. A separate 100-policy grid search finds no tested recharge-pumping-timing policy that eliminates future burden, whose minimum remains 0.532193531 model-volume units, despite zero present requirement. Formal counterexamples separate HDC from simplified present-viability, adaptation-tipping, real-option, and robust-control signals. The contribution is not a new desalination technology or hydrological solver, but a decision quantity distinguishing present sufficiency from future avoidability. Results support HDC as a reproducible planning diagnostic while explicitly limiting “unavoidable” to the modeled policy set and horizon.