EPA Research Partner Support Story: Microbial Treatment Targets for Water Reuse
Partner: Washington State Department of Health (DOH)
Challenge: Determining the correct treatment targets to enable onsite water reuse in Washington State
Resource: Scientific report providing risk-based framework and associated pathogen reduction targets
Project Period: 2022 – 2025
Onsite water reuse continues to gain traction throughout the United States, presenting multi-faceted benefits to both water supply and wastewater management. Without federal regulations or guidelines for onsite water reuse, states pursuing these new opportunities are faced with developing regulatory policies that protect public health. The novelty of decentralized treatment for onsite use and its unique technical and management configurations have presented practical challenges to developing these programs.
“The high-quality research and reports produced by EPA’s ORD allow our agency to be more efficient and more effective with state resources. I cannot stress the importance that the respected, defensible, non-commercial science experts at ORD and their work products have had on enabling our department to move forward with ONWS [onsite nonpotable water systems] regulations.” – Washington State Department of Health, Office of Drinking Water, Engineering and Technical Service Steve Deem
Through partnerships such as the National Blue Ribbon Commission for Onsite Non-Potable Water Systems, EPA’s Office of Research and Development (ORD) provides technical support to states seeking risk-based treatment approaches for water reuse, including onsite systems. State regulators have specifically asked for scientific information on appropriate fit-for-purpose pathogen log reduction targets (LRTs) for water reuse applications. Notably, the state of Washington expressed interest in using a disability-adjusted life year (DALY) metric, which is commonly used internationally and allows comparison against other management objectives such as chemical risk control.
In January 2025, ORD, in collaboration with the Office of Water’s Water Reuse Program, completed this request through publication of the scientific report Risk-Based Framework for Developing Microbial Treatment Targets for Water Reuse. This peer-reviewed EPA resource outlines a modeling process that states and other jurisdictions can utilize to develop scientifically defensible water reuse treatment targets and provides state-of-the-science parameter input values. Critically, the report also includes computed log reduction targets (LRTs) using the current inputs which states may choose to utilize directly, avoiding the cost and time of developing their own targets. This provides the option for states to choose either the available numbers or to incorporate their own data and perspectives according to local context.
Washington is among the first states to directly utilize the new reference, using its DALY-based targets in their draft proposal for onsite non-potable use to provide a firm and defensible technical basis to inform their proposed rules. Washington state government recognizes the advantages of using a DALY metric as basis for the risk assessment to support cost-benefit evaluations relative to other management goals. ORD continues its outreach to support additional states seeking information on this topic.