WATER SOURCES AND DRAINAGE
Major rivers in the East district are Teesta or Tista and Rangit. Teesta can be called as Ganga of the state of Sikkim as most of the Sikkim’s settlements are found along the banks of this river. The Teesta comes out as a snout from the Zemu glacier above Lachen Gompha. The Lhonk stream from the north joins it. Another stream Lachung rises from Pauhunri and meets the Teesta at Chumthang. The minor rivers in the district areRani Khola, Busuk Khola, Rishi Khola and Ratey Chu.
WATER SOURCES AND DRAINAGE SYSTEM
Urban households in the district are supplied by the central water system maintained and operated by the Public Health and Engineering Department (PHED). The main source of PHED water supply is the Rateychu River located about 16 km (9.9 mi) from the city, at an altitude of 2,621 m (8,599 ft). Its water treatment plant is located at Selep. The river Rateychu is snow-fed and has perennial streams. Since there is no habitation in the catchment area except for a small army settlement, there is little environmental degradation and the water is of very good quality. 40 seasonal local springs are used by the Rural Management and Development Department of Sikkim Government to supply water to outlying rural areas. The entire city drains into the two rivers, Ranikhola and Roro Chu, through numerous small streams and Jhoras. Ranikhola and Roro Chu rivers confluence with Teesta River, the major source of drinking water to the population downstream. The densely populated urban area of Gangtok does not have a combined drainage system to drain out the storm water and waste water from the buildings. The estimated solid waste generated in Gangtok city is approximately 45 tonnes. Only around 40% of this is collected by UDHD, while the remainder is indiscriminately thrown into Jhora, streets and valleys. The collected waste is disposed in a dump located about 20 km (12 mi) from the city. There is no waste collection from inaccessible areas where vehicles cannot reach, nor does any system of collection of waste exist in the adjoining rural areas. The city is under a statewide ban on the use of polythene bags.East district is mainly drained by the perennial Tista river with tributaries Dik Chhu, Rate Chhu and Rangpo Chhu. The cultivation is done mainly by springs and surface water from Kholas.