This document provides information on costs and performance characteristics of treatment technologies that EPA projects public water systems (PWSs) will use to comply with the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) and the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). The unit costs are based on design criteria relevant to compliance with these rules. EPA developed these costs as part of making a regulatory impact assessment. The Stage 2 DBPR will require PWSs that produce high concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) to reduce the levels of those species. Specifically, PWSs would have to comply with a locational running annual average (LRAA) of 80 and 60 (micro)g/L for TTHM and HAAs, respectively. THMs and HAAs form primarily through reactions between chlorine, which is applied as a disinfectant, and natural organic matter in water. Systems can reduce the formation of THMs and HAAs by either of two general approaches: (1) reduce the concentration of dissolved organic carbon prior to disinfection through processes like enhanced coagulation, activated carbon, or nanofiltration, or (2) use pathogen removal/inactivation processes that do not form, or form low concentrations of, THMs and HAAs. Such processes include disinfection via chloramines, ozone, chlorine dioxide, ultraviolet (UV) light, and the use of membranes. The LT2ESWTR will require certain PWSs to provide additional removal or inactivation of Cryptosporidium. The amount of required additional treatment for a PWS is dependent upon the results of source water Cryptosporidium monitoring and the existing level of treatment. Systems can treat for Cryptosporidium by: (1) removing Cryptosporidium through filtration processes, like granular media filtration, cartridge filters, or membranes; or (2) using disinfectants that are effective against Cryptosporidium, such as chlorine dioxide, UV, and ozone. Chlorine and chloramines are largely ineffective at inactivating Cryptosporidium. Because many of the technologies systems can use to treat for Cryptosporidium are also effective in reducing formation of THMs and HAAs, EPA has chosen to address technologies for both the Stage 2 DBPR and LT2ESWTR in a single document.