Abstract:

Water is required for the production of nearly all goods. The water used in the production process of an agricultural or industrial product is called the ‘virtual water’ contained in the product. If one region exports a waterintensive product to another region, it exports water in virtual form. In this way some regions support other regions in their water needs. For waterscarce regions it could be attractive to achieve water security by importing waterintensive products instead of producing all waterdemanding products locally. Reversibly, waterrich regions could benefit from their abundance of water resources by producing waterintensive products for export.
Water footprint concept is closely linked to the virtual water concept. The water footprint concept has been developed in order to have an indicator of water use in relation to consumption of people. The water footprint of a region is defined as the volume of water needed for the production of the goods and services consumed by the inhabitants in the region. The internal water footprint of a region is the volume of water used from the local water resources to produce the goods and services consumed by the inhabitants in the region. The external water footprint of a region is the volume of water used in other regions to produce goods and services imported and consumed by the inhabitants in the region. The water footprint of a region can be assessed by taking the use of the local water resources, subtracting the virtual water flow that leaves the region and adding the virtual water flow that enters the region.
Based on the theories and methods of the virtual water and the water footprint, the concept of the urban water footprint was put forward and the calculation model of the urban water footprint was established, which was used to calculate the utilization of water resources of the Shanghai and Chongqing from 1999 to 2008 in order to reveal the effects and its differences of social and economic development on water resources system. The results showed that the total water footprint of Shanghai and Chongqing both showed an increasing tendency, and the gap between them was reducing in the recent decade. The water footprint structure changed little in Chongqing, while the proportion of virtual water net input quantity grew rapidly in Shanghai. Besides, the utilization of water resources was overloaded seriously in Shanghai, which was in a safe state in Chongqing. The selfsufficiency capacity of water resources was low in Shanghai, and the dependence on outside was much higher than Chongqing. Moreover, the efficiency in water resources utilized in Chongqing was much lower than Shanghai. Finally, several countermeasures to ensure the safety of urban water resources were proposed from the perspective of consumers, producers and managers