The sign on left indicates it is Field #1 and the sign on right describes the purification method and steps using potassium aluminum sulfate to clean the water. The field is located on the grounds of the Orthopedic Center, run by Surgeon General Robert K.S. Lim, who studied and promoted sanitary science in China.
Source of Descriptive Information
Forman, H. (1948). Changing China. New York: Crown Publishers.