Still they are voliating 6 international law and treaty is legally binding not like something they do them self and throw in the dustbin. Otherwise, there is no agreement in any part of the world. It is a law and international law.
@Fatman17 posted an article on that and author explained that indus water treaty is a biding and cannot be breach as there is no scope of suspension or ending the agreement which gives Pakistan legal reason to strike india indus infrastructure.
Pakistan knew one fine day India would brech indus water that is why Pakistan has invested in nuclear so that if Pakistan goes down than it ensure it takes india down with it.