لَا يَصْلُحُ تَوْزِيعُ الْمَاءِ إِلَّا بِالْعَدْلِ.
Water distribution cannot be sound without fairness.
The negative-except construction makes fairness necessary for a sound distribution. It does not say that naming fairness alone settles every logistical concern: a necessary condition is not automatically sufficient.
Against an unfair proposal, the restriction becomes pointed. First state exactly what is necessary, then consider whether the discourse supports correction of an opposing belief or another specialized function.