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This chapter analyses the demand for, and supply of, water to Shanghai in relation to water quality and variations in availability. The population of Shanghai is growing rapidly. This and declining water quality in its traditional water supply sources has forced Shanghai to become mainly reliant on water from the Changjiang. Since annual water demand is 0.55 per cent of the river’s flow, the Shanghai government does not manage demand for water in the city. Meeting rising demand is dependent on maintaining and expanding the extraction, treatment and supply systems that are ageing and not capable of delivering potable water to consumers. Low flows in the winter season raise the risk of saltwater intrusions, disrupting the system (which has limited storage capacity). The complex intergovernmental responsibilities for water allow other agencies to build water projects (e.g. the South–North Water Transfer System) that are detrimental to Shanghai without considering Shanghai’s situation.

Shanghai is critically dependent on the Changjiang, China’s largest river, for its water supply. The flow is very stable from year to year but has strong seasonal variation with 70 per cent of flow in the summer season. The total flow is robust in the face of significant human influences. The annual flow is 900 billion cubic metres and only 0.55 per cent of this is taken for Shanghai’s water supply. No significant threats exist to the total volume of water available but there are threats from seasonal low flows, diversions of water to other users, deteriorating water quality and salt water intrusions that affect the main water supply intakes for Shanghai. The operation of the Three Gorges Dam has induced changes to the monthly flow regime, reducing flows in October to fill the dam before the low flow season and raising flows January to March as that water is used for power generation.

Chapter 4 explains the properties of China’s system of water management, as it relates to water supply in Shanghai. The chapter treats this system as an outcome of scale-making, in which socio-environmental regions – such as basins or jurisdictions – are constructed to serve water politics. The chapter introduces in turn China’s administrative hierarchy, with its divisions of responsibilities between ministries and overlapping responsibilities between different levels of government. New scales of government have emerged, such as river basin commissions and other reorganisations at a more local scale, and new attempts to manage the use of water and levels of pollution. The scales over which governments exercise power are being altered, partially in response to the scales at which corporations, non-government organisations and corporations act.