In this document, EPA is finalizing the Interim Enhanced Surface Water Treatment Rule (IESWTR). The purposes of the IESWTR are to: Improve control of microbial pathogens, including specifically the protozoan Cryptosporidium, in drinking water; and address risk trade- offs with disinfection byproducts. Key provisions established in today's final IESWTR include: A Maximum Contaminant Level Goal (MCLG) of zero for Cryptosporidium; 2-log Cryptosporidium removal requirements for systems that filter; strengthened combined filter effluent turbidity performance standards and individual filter turbidity provisions; disinfection benchmark provisions to assure continued levels of microbial protection while facilities take the necessary steps to comply with new disinfection byproduct standards; inclusion of Cryptosporidium in the definition of ground water under the direct influence of surface water (GWUDI) and in the watershed control requirements for unfiltered public water systems; requirements for covers on new finished water reservoirs; and sanitary surveys for all surface water systems regardless of size. The IESWTR builds upon the treatment technique requirements of the Surface Water Treatment Rule. EPA believes that implementation of the IESWTR will significantly reduce the level of Cryptosporidium in finished drinking water supplies through improvements in filtration. The Agency estimates that the likelihood of endemic illness from Cryptosporidium will decrease by 110,000 to 463,000 cases annually. The Agency believes that the rule will also reduce the likelihood of the occurrence of outbreaks of cryptosporidiosis by providing a larger margin of safety against such outbreaks for some systems. In addition, the filtration provisions of the rule are expected to increase the level of protection from exposure to other pathogens (i.e., Giardia or other waterborne bacterial or viral pathogens). The IESWTR applies to public water systems that use surface water or GWUDI and ser