[Centurion2000]

I believe the "death of the subcontinent" was referring to radioactive contamination of the Himalayan water sources for most of the area's population. This would indeed be devastating.

Put the water into a tank, let the sediment settle; skim the water off the top down to the last 1/4 of the tank.

No contamination.

[Restorer]

I suspect your approach is somewhat impractical for irrigation water, which is what the vast majority of this water is used for. Or perhaps the radioactivity will settle out in the slow-moving stretches of the rivers once they reach the plains. I don't know what the possible consequences of a massive accumulation of radioactivity in the riverbeds of India/Pakistan might be.

[lawdude]

"No contamination."

Irradiated water would probably be the cleanest drinking water these fools have ever had! No fluorine needed, either!