Beijing suffers from a severe lack of water: the quantity of water available per head is only one-thirtieth of the global average. Guanting Reservoir, the first major reservoir to be built after 1949, drew water from a 43,000-square-kilometre basin. Once completed, it provided a total of 39.6 billion cubic metres of water and irrigated 1.1 million mu (734 square kilometres) of land. However, upstream industrial and economic activity reduced the flow and polluted the water. The quality of the water fell to class five or worse, which forced Beijing to stop drawing water from Guanting in 1985. The city now takes its water from the Miyun and Huairou reservoirs. But the outlook for the Miyun Reservoir is not good: the amount of water it can supply is plummeting, and it suffers from an excess of nutrients. As well as the dumping of excrement, this is also caused by the surface run-off from fertilisers and pesticides.