U.S. Code of Federal Regulations

Regulations most recently checked for updates: Aug 27, 2025

All TitlesTitle 40Chapter IPart 141Subpart T - Subpart T—Enhanced Filtration and Disinfection—Systems Serving Fewer Than 10,000 People

GENERAL REQUIREMENTS
§ 141.500 - General requirements.
§ 141.501 - Who is subject to the requirements of subpart T?
§ 141.502 - When must my system comply with these requirements?
§ 141.503 - What does subpart T require?

FINISHED WATER RESERVOIRS
§ 141.510 - Is my system subject to the new finished water reservoir requirements?
§ 141.511 - What is required of new finished water reservoirs?

ADDITIONAL WATERSHED CONTROL REQUIREMENTS FOR UNFILTERED SYSTEMS
§ 141.520 - Is my system subject to the updated watershed control requirements?
§ 141.521 - What updated watershed control requirements must my unfiltered system implement to continue to avoid filtration?
§ 141.522 - How does the State determine whether my system's watershed control requirements are adequate?

DISINFECTION PROFILE
§ 141.530 - What is a disinfection profile and who must develop one?
§ 141.531 - What criteria must a State use to determine that a profile is unnecessary?
§ 141.532 - How does my system develop a disinfection profile and when must it begin?
§ 141.533 - What data must my system collect to calculate a disinfection profile?
§ 141.534 - How does my system use this data to calculate an inactivation ratio?
§ 141.535 - What if my system uses chloramines, ozone, or chlorine dioxide for primary disinfection?
§ 141.536 - My system has developed an inactivation ratio; what must we do now?

DISINFECTION BENCHMARK
§ 141.540 - Who has to develop a disinfection benchmark?
§ 141.541 - What are significant changes to disinfection practice?
§ 141.542 - What must my system do if we are considering a significant change to disinfection practices?
§ 141.543 - How is the disinfection benchmark calculated?
§ 141.544 - What if my system uses chloramines, ozone, or chlorine dioxide for primary disinfection?

COMBINED FILTER EFFLUENT REQUIREMENTS
§ 141.550 - Is my system required to meet subpart T combined filter effluent turbidity limits?
§ 141.551 - What strengthened combined filter effluent turbidity limits must my system meet?
§ 141.552 - My system consists of “alternative filtration” and is required to conduct a demonstration—what is required of my system and how does the State establish my turbidity limits?
§ 141.553 - My system practices lime softening—is there any special provision regarding my combined filter effluent?

INDIVIDUAL FILTER TURBIDITY REQUIREMENTS
§ 141.560 - Is my system subject to individual filter turbidity requirements?
§ 141.561 - What happens if my system's turbidity monitoring equipment fails?
§ 141.562 - My system only has two or fewer filters—is there any special provision regarding individual filter turbidity monitoring?
§ 141.563 - What follow-up action is my system required to take based on continuous turbidity monitoring?
§ 141.564 - My system practices lime softening—is there any special provision regarding my individual filter turbidity monitoring?

REPORTING AND RECORDKEEPING REQUIREMENTS
§ 141.570 - What does subpart T require that my system report to the State?
§ 141.571 - What records does subpart T require my system to keep?
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