Earlier quoted context omitted.
Do you think (plausibly) threatening to cut off water to large swathes of Pakistan, or blowing up some random terrorist camps, is the bigger actual threat?
Cutting off water supply is clearly the bigger threat. However, it involves a longer time frame - building infrastructure which one expects not to use in a normal situation. Importantly, even once built, it selects the wrong targets, not terrorists or military bases - but regular people who will be faced with scarcity of water and food, as the crops use Indus water. This would be something highly unethical, and also…
Even if it were to translate to sanctions, I'm not so sure BJP wouldn't welcome it. "The Fatherland is besieged, let's unite together around Dear Leader and fight back like one" tends to be a very popular take in authoritarian countries for a reason, and it's that much easier to pull off when you can actually point at some way in which your country is targeted.