The third edition of Groundwater, AWWA Manual M21, is newly designed and fully updated to give operators, engineers, and other water supply professionals a comprehensive understanding of groundwater. The manual provides a basic understanding of groundwater characteristics - its movement, quality, and geology - and the impact these characteristics have on the design, construction, and maintenance of groundwater-well systems for water supply. Additionally, this manual will help water supply professionals answer many of the questions they have about complex aquifer systems, quality testing, pumps and pumping systems, contamination, and treatment.