Rubbish.
Chinese cannot screw us for the simple reason that Tibet is relatively uninhabited and there is no one to consume that water
Second water cannot be stored forever, the dam will overflow
Third, there is perma frost in Tibet so its neither cheap nor easy to do construction there.
Fourth, The mighty Himalayan ranges surround the Bhrama kund, so that water is not going anywhere.
Fifth, water will freeze at that temperature so its not that easy to transport it elsewhere
Sixth, Water can only flow downhill
....... and that will mean into India.
If the chinese really wanted to screw us on water, they will simply have to spend hundreds of billions of $ to do so. It would be cheaper to buy more aircrafts and missiles