This manual is a technical reference guide in designing, installing, operating, and maintaining reservoirs using flexible-membrane materials for linings and floating covers. Source information was gathered by reviewing and collecting the experience of designers, manufacturers, and owners of flexible-membrane products that were introduced to the water industry in the early 1950s. It is not intended to be a design handbook or the equivalent of an AWWA standard; rather, it should serve as a technical reference document to be used in conjunction with AWWA D130, Standard for Flexible-Membrane-Lining and Floating-Cover Materials for Potable Water Storage.