One of the fundamental responsibilities of management is the establishment of a continuing program to insure the reliability and validity of analytical laboratory and field data gathered in water treatment and wastewater pollution control activities. This handbook is addressed to laboratory directors, leaders of field investigations, and other personnel who bear responsibility for water and wastewater data. Subject matter of the handbook is concerned primarily with quality control for chemical and physical tests and measurements. Sufficient information is offered to allow the reader to inaugurate, or to reinforce, a program of analytical quality control which will emphasize early recognition, prevention and correction of factors leading to breakdowns in the validity of data. (Author)