THE Permanent Court of Arbitration’s supplemental award on Islamabad’s decade-old petition challenging the design specifications of two Indian hydropower projects on rivers allocated to Pakistan under the Indus Waters Treaty is a definitive affirmation of the supremacy of international law over unilateral state actions. It places India in an increasingly untenable position — legally, diplomatically, and perhaps important, morally. The ruling removes whatever ambiguity India has been trying to exploit.