USEPA developed The Membrane Filtration Guidance Manual in support of the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), which has identified membrane filtration (i.e., MF, UF, NF, RO, and membrane cartridge filtration (MCF)) as one category of treatment technology in a “toolbox” of options that may be used to achieve the required level of Cryptosporidium treatment. Although the LT2ESWTR only regulates membrane filtration in terms of its application for compliance with the requirements of the rule, the concepts and guidance provided in this manual may also be relevant to the Interim Enhanced Surface Water Treatment Rule (IESWTR), the Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR), the Ground Water Rule (GWR), and other regulations, at the discretion of the State.