Effective in 1991, the Surface Water Treatment Rule (SWTR) applies to all waterworks that use surface water or groundwater under the direct influence (GUDI) of surface water. The rule established treatment techniques in lieu of maximum contaminant levels for Giardia lambia, viruses, heterotrophic plate count bacteria, Legionella, and turbidity. The rule requires 99.9 percent (3-log) removal and/or inactivation of Giardia cyst through filtration, and 99.99 percent (4-log) removal and/or inactivation of viruses through disinfection.
Effective in 2002, the Interim Enhanced Surface Water Treatment Rule (IESWTR) applies to surface water or groundwater under the direct influence of surface water sources that serve a population of 10,000 or more. The IESWTR builds on the Surface Water Treatment Rule by adding protection from Cryptosporidium. The rule is designed to optimize treatment reliability and enhance physical removal efficiencies to minimize the Cryptosporidium levels in finished drinking water. The rule established a MCLG of zero for Cryptosporidium and requires 99 percent (2-log) removal requirements for systems that filter. The IESWTR requires sanitary surveys for all waterworks (regardless of size) using surface water or groundwater under the direct influence of surface water. The Rule also requires covers for all new finished water storage facilities and includes disinfection profiling and benchmarking provisions to ensure systems provide continued levels of microbial protection while taking the necessary steps to comply with the Disinfection By-Products standards.
Effective in 2002, the Long-term 1 Enhanced Surface Water Treatment Rule (LT1) extends the IESWTR to apply to waterworks serving less than 10,000 people.
Effective in 2006, the Long-term 2 Enhanced Surface Water Treatment Rule (LT2) applies to surface water and groundwater under the direct influence of surface water sources and requires monitoring of Cryptosporidium.
Interim Enhanced Surface Water Treatment Rule: A Quick Reference Guide. (PDF)
Long-Term 1 Enhanced Surface Water Treatment Rule: A Quick Reference Guide (PDF)
Long-Term 2 Enhanced Surface Water Treatment Rule: A Quick Reference Guide for Schedule 1 Systems. (PDF)