The source of four mighty rivers—the Indus, Brahmaputra, Salween and Mekong—is in China-controlled Tibet. But Beijing has until now carefully ‘calibrated’ its approach to sharing water with its downstream neighbours. The calibration depends on the ‘quality of the political relationship’ with that country, so India and Vietnam come off second or even third best since they have difficult ties with China. Beijing will not share data on the rivers flowing into these two countries, more so during the dry season. It will charge money from one country while giving the same data to another neighbour for free. It will not be governed by any international law nor join any treaty that could limit its ability to manipulate the flow of waters downstream for its maximum political and economic benefit.