Abstract: Water resource is regarded as a complex system and is quantitatively analyzed by using the theory and method of emergy. The water system in Taihu Lake watershed is taken as a research object. Emergy system diagrams and emergy analytical tables were obtained and the emergy transformity of water supply resource of the watershed from 2007 to 2011 was calculated. Result shows that the emergy transformity of the watershed’s water resource has a tendency of increasing over years, which is consistent with the practice of intensifying regulation projects to improve water environment. Besides, the emergy transformity of water resource under human disturbance increased by 24.3% on the average compared with the natural condition, and the increment displays a trend of increasing year by year as well, from 4.31% in 2007 to 36.4% in 2011, indicating that safe water supply takes more cost despite the rich water resource of the watershed, and that water shortage of water-quality type is a new challenge of the century.

Key words: water resources, complex system, energy, emergy, emergy transformity