Microbial and DBP Rule Revisions: Balancing Risks

The US Environmental Protection Agency (EPA) continues to work toward proposing revisions for Microbial and Disinfection Byproduct (MDBP) rules next year. These potential rule revisions are focused on the Surface Water Treatment Rules and Stage 1 and Stage 2 Disinfectants and Disinfection Byproduct Rules, covering eight contaminant candidates: (1) chlorite, (2) Cryptosporidium, (3) haloacetic acids, (4) heterotrophic bacteria, (5) Giardia lamblia, (6) Legionella, (7) total trihalomethanes, and (8) viruses.

Since the Safe Drinking Water Act (SDWA) became law in 1974, US drinking water supplies have made monumental advances in protecting the public from microbial risks. This is, in part, thanks to a suite of seven MDBP rules that since 1996 have driven how water systems manage and balance these risks.

EPA is developing a proposed rulemaking, with the goal of publishing a proposal in summer 2025 and finalizing those revisions by February 2028. EPA is expected to complete required engagements with organizations representing state/local officials and small water systems in accordance with the Unfunded Mandates Reform Act, Executive Order 13132—Federalism, and the Small Business Regulatory Enforcement Fairness Act, respectively. Following these consultations, EPA will send the proposed rulemaking revising these rules to the White House Office of Management and Budget for review before publication.

AWWA's Government Affairs Office has worked with EPA and expert volunteers throughout this process, including hosting a series of workshops on MDBPs this summer to inform AWWA recommendations on the proposed rulemaking. Two of these workshops brought together subject matter experts, water utilities, and state regulators to discuss available data and potential revisions supported by the data. The third workshop allowed attendees to discuss potential revisions, available data, and research needs.

These discussions highlighted opportunities for EPA to enhance public health protection through rule revisions. There was broad support in the workshops for requiring certain water systems to conduct regular inspections of tanks for deficiencies that may threaten public health, establishing a minimum numeric secondary disinfectant residual level, and ensuring consecutive systems have the capacity to comply with water quality standards.

However, these discussions also emphasized the need for potential revisions to thoroughly consider the data (or lack thereof) to support potential revisions. Additionally, the discussions stressed the importance of considering both state regulator and utility staff capacity to implement the revised standards.

AWWA plans to continue working with EPA staff, state regulators, and expert volunteers, including representing water utilities as part of the consultations EPA is hosting with local officials and small water systems. These efforts will further support the rulemaking process with technical analysis of data and through the development of recommendations that achieve improvements to public health protection while balancing other priorities for water utilities. It will also be important to balance risk trade-offs between microbial reduction and DBP formation.