I didn't have time to dig on Friday, but here's a great article giving an overview of water use and the cotton sector in Xinjiang (also linking the 2017 China-caused price spike to the developments of Xinjiang cotton):

"Agriculture in Xinjiang is almost totally dependent on irrigation. However, Xinjiang is one of the Chinese provinces with the most serious water shortage." and "Since 2000, the cotton planting area in Xinjiang has shown a fluctuating and increasing trend. Encouraged by the increase of cotton price and government subsidies, the cotton planting area increased significantly after 2017, and the cotton planting area almost reached a maximum."

http://www.world-agriculture.net/article/evaluation-of-cotton-production-under-limited-water-resources-in-the-arid-region-of-xinjiang-china