This standard pertains to flexible-membrane materials supplied in sheet form for lining, covering, or lining and covering potable water reservoirs. The successful application of this standard is dependent on an appropriate site evaluation, design, material selection, construction, as well as operations and maintenance. This standard includes requirements for material properties, fabrication, and installation. Major revisions made to the standard in this edition include the following: use of NSF 54 - previous editions of this standard contained references to NSF 54 (NSF 54 has since been rescinded, necessitating a revision to this document), material previously incorporated by reference to NSF 54 has been added with this revision; and, this standard has been rewritten in its entirety to incorporate current industry practice and newly developed materials.