The Ratey Chu is a river in the Indian state of Sikkim that is the main source of water for the state capital, Gangtok. The Ratey Chu emerges from the glacier-fed Tamze lake at an elevation of 12500feet above sea level. The Ratey Chu is tapped for drinking water at an elevation of 8200feet. From this tapping point or water supply head work, water is transported 17km (11miles) to the Selep Water Treatment Plant site.