There were four water treatment plants in Shangjing. These four water treatment plants supplied water to the entire city of Shangjing other than the Imperial City.
The young man who bought the book had entered the White Dragon Cave water treatment plant, which was located near the White Dragon Cave reservoir to the West of Shangjing. This water treatment plant supplied water to a quarter of the people in Shangjing.
As the situation in Shangjing was a little tense, the water treatment plant had adopted the highest security measures. Outsiders were not allowed to enter the plant. Even the staff who entered the plant could see that the ground was divided into three routes, which were red, yellow, and blue.
