The goal was to compare water usage in cities like Shanghai and Chongqing by looking at the water used to make goods. This "virtual water" gets moved around when products are traded. For water-scarce places, importing water-heavy items can help balance water needs, while water-rich areas can export water-heavy goods. They studied the water footprints of the two cities from 1999 to 2008, using a model they created. Results showed that both cities used more water over time, with the gap between them shrinking. Chongqing's water footprint structure stayed mostly the same, while Shanghai's had some changes.