It would be impossible for the Chinese to steal the waters of the Brahmaputra, the river system is ginormous starting from the Lohit in Arunachal to the Teesta in West Bengal, Yarlung Tsangpo the parent river is just like a hill stream as it passes through Tibet, once it debouches into India via the Namcha Barwa gorge it becomes the mighty Brahmaputra that the world knows of. There are countless streams draining from Bhutan, Arunachal and Assam into the Brahmaputra which are both rain fed and supported by glacial melt water, and the north east India is amongst the rainiest places on earth.
The stupid Chinese know that very well, and the worst they are doing is keeping up with their tradition of environmental pollution by discharging toxic industrial effluents into the pristine waters of the Siang in Arunachal.