The growing emphasis on water quality standards, enforcement, and monitoring requires the establishment and effective operation of a quality assurance (QA) program to substantiate the validity of analytical data. This revised section contains general guidelines for developing a Quality System designed for the laboratory’s QA program and for intralaboratory and interlaboratory quality control (QC) activities, as well as guidance for developing a laboratory Quality Manual. The revised text also provides new information on biosafety criteria and generally updates QC information for laboratory equipment, instrumentation, supplies, and established methods. In addition, 9020 also explains how to validate new or nonstandard methods, and how to handle data. Extensive references are included.