Onsite Non-Potable Water Reuse Research

• Risk-Based Modeling
• Monitoring of Treatment Performance
• Life Cycle Assessment
• Collaboration
• Related Resources

---

Increasing pressures on water resources have led to greater water scarcity and a growing demand for alternative water sources. Onsite non-potable water reuse is one solution that can help communities reclaim, recycle, and then reuse water for non-drinking water purposes. Onsite non-potable water reuse systems (ONWS) capture and treat water sources generated from within or surrounding a building, such as wastewater, greywater, stormwater, or roof collected rainwater. The treated water is then reused onsite or locally.

The National Water Reuse Action Plan (WRAP) was developed in collaboration with other federal agencies, states, tribes and water sector stakeholders to drive the progress of water reuse to meet increasing demands for sufficient quantities of high-quality water. EPA’s research supports the implementation of the WRAP by developing and enhancing methods and treatment strategies for onsite water reuse. EPA is collaborating with states and utilities who are facilitating the development of ONWS to define treatment and monitoring approaches that will ensure safe adoption and to build the utility business case for implementing such systems.

About Onsite Non-Potable Water Reuse Systems

Within a building, several water sources are generated that can be treated and used onsite or in a local area for non-drinking water purposes, such as toilet flushing, clothes washing, and ornamental plant irrigation. 

Risk-Based Modeling

EPA researchers are conducting risk-based modeling to understand the human health risks associated with onsite reuse of locally-collected waters, such as wastewater, greywater, stormwater, and roof-collected rainwater, for non-potable applications in and around buildings. Quantitative Microbial Risks Assessment (QMRA) models were developed to characterize potential risks associated with these systems and to define the levels of pathogen removal needed to perform reuse safely. These reduction targets, reported for each of the three major groups of waterborne pathogens (viruses, bacteria, and protozoans) across various combinations of water sources and end uses, provide specific performance metrics for treatment systems.

Increasing pressures on water resources have led to greater water scarcity and a growing demand for alternative water sources. Onsite non-potable water reuse is one solution that can help communities reclaim, recycle, and then reuse water for non-drinking water purposes. Onsite non-potable water reuse systems (ONWS) capture and treat water sources generated from within or surrounding a building, such as wastewater, greywater, stormwater, or roof collected rainwater. The treated water is then reused onsite or locally for non-drinking purposes, such as toilet flushing, clothes washing, and ornamental plant irrigation.

This research also includes the evaluation of initial pathogens concentrations in different onsite water sources as well as modeling the risks associated with proposed treatment options and ONWS cross-connections.

Research Publications

• Characterization of Roof Runoff Microbial Quality in Four U.S. Cities with Varying Climate and Land Use Characteristics (2022). This study describes the microbial quality of roof runoff (rainwater) collected across different geographic regions of the U.S. New pathogen measurement data can be used to inform risk assessments of onsite rainwater capture and use, including the development of appropriate treatment targets.
• Quantitative Microbial Risk Assessment of Antimicrobial Resistant and Susceptible Staphylococcus aureus in Reclaimed Wastewaters (2021). In addition to enteric pathogens, skin-associated organisms such as Staphylococcus aureus can be concerns during water reuse. This study assessed whether treatment targets developed for the management of enteric pathogens would also be protective of S. aureus and methicillin-resistant S. aureus (MRSA). The latter required novel additions to the QMRA model to account for its resistance to antibiotic treatment, including genetic exchange processes, delayed health impacts following colonization. and the differential burden of resistant infections. Results show that when using a disability-adjusted life-year (DALY) metric, only minimally treated waters would exceed the selected health benchmark for MRSA.
• Enteric Pathogen Treatment Requirements for Non-Potable Water Reuse Despite Limited Exposure Data (2020). Ingestion volumes of water during common non-potable uses such as toilet flushing and irrigation are uncertain and variable. This research assessed the sensitivity of previously-modeled treatment targets to these input parameters, demonstrating relative insensitivity when including an accidental ingestion factor in the analysis. Additionally, it demonstrated that other water uses such as decorative fountains and vehicle washing could also safely employ non-potable waters treated to existing targets.
• A Risk-Based Evaluation of On-Site, Non-Potable Reuse Systems Development in Compliance with Conventional Water Quality Measures (2020). Risk-based treatment requirements are an alternative to conventional end-point performance metrics such as a specified level of fecal indicator bacteria in effluent. To compare the approaches, this work modeled the rick associated with systems approved under the NFP-350 certification and demonstrated that they may not meet risk-based criteria for viral and protozoan pathogens.
• Droplet Digital PCR Quantification of Norovirus and Adenovirus in Decentralized Wastewater and Graywater Collections: Implications for Onsite Reuse (2020). Previous QMRA to develop treatment targets relied of simulated pathogen densities in onsite wastewater and graywater, given the lack of empirical data on these systems. This study addressed the data gap by collecting new measurement of viral pathogens in several onsite systems, demonstrating the potential for high and variable pathogen loads in these wastewaters.
• Human Health, Economic and Environmental Assessment of Onsite Non-Potable Water Reuse Systems for a Large, Mixed-Use Urban Building (2020). This study used quantitative microbial risk assessment, life cycle assessment, and life cycle cost analysis to characterize the human health, environmental, and economic aspects of onsite non-potable water reuse systems. The use of multiple metrics allows for identification of weaknesses in systems that lead to burden shifting and provides balanced decision making.
• Human Health Impact of Cross-Connections in Non-potable Reuse Systems(2018). QMRA was used to estimate the microbial risks from two contamination pathways in ONWS: (1) contamination of potable water by (treated) reclaimed, non-potable water, and (2) contamination of reclaimed, non-potable water by wastewater or greywater.
• Human Health Impact of Non-Potable Reuse of Distributed Wastewater and Greywater Treated by Membrane Bioreactors (2018). The annual probability of infection resulting from non-potable exposures to distributed greywater and domestic wastewater treated by an aerobic membrane bioreactor (MBR) followed by chlorination was assessed. A probabilistic QMRA was conducted for both residential and office buildings and a residential district using Norovirus, Rotavirus, Campylobacter jejuni, and Cryptosporidium spp. as reference pathogens. 

Monitoring of Treatment Performance

Monitoring the treatment processes in ONWS is necessary to ensure that recycled water is treated appropriately to reduce pathogens for safe application. Since pathogen monitoring is inefficient, other non-pathogenic microorganisms are being investigated to stand in for pathogens. This research involves describing and quantifying the microorganisms, both bacterial and viral, found in these locally-collected wastewaters. In addition, the alternative microorganisms are evaluated to ensure they are removed in a similar way as pathogens are during ONWS treatment. The use of alternative microorganisms will facilitate monitoring of ONWS to verify that treatment systems are performing as intended.

Research Publications

• Understanding Microbial Loads of Wastewater Treatment Works as Source Water for Water Reuse (2021). The main objective of this study was to assess the microbial quality of reclaimed water. In addition, we attempted to address the efficacies of treatment process typically employed in municipal wastewater treatment plants, focusing on the removal or inactivation of waterborne pathogens from the influent to the effluent. This study will assist municipalities considering wastewater effluent as another source of drinking water with important data on the prevalence, occurrence, and persistence of waterborne pathogens of concern. More importantly, the results from this study will aid in building a richer microbial occurrence database that can be used towards revisiting reuse guidelines and disinfection practices for water reuse practices.
• Reducing Inherent Biases Introduced During DNA Viral Metagenome Analyses of Municipal Wastewater (2018). This study was conducted to understand the inherent variability introduced when conducting viral metagenomic analyses of wastewater and provide a bioinformatic strategy to accurately analyze sequences for viral community analyses.

Life Cycle Assessment

While local entities have identified a number of drivers for implementing ONWS, ranging from addressing water scarcity to the development of green space within urban areas, quantifiable data is needed on the life cycle impacts and costs to build the business case for implementation. From the perspective of the local utility or government, the implementation of ONWS must account for the costs of installing and operating the ONWS to the benefits derived (e.g., avoided drinking water costs). To provide insight into this system level perspectives, life cycle costs and impacts were assessed for ONWS of various scales and types.

Research Publications

• Onsite Non-Potable Reuse for Large Buildings: Environmental and Economic Suitability as a Function of Building Characteristics and Location (2021). This study describes and utilizes NEWR to explore the potential of four source waters for a variety of building configurations throughout the United States. Results describe prominent geographic trends and comparative results between source waters.
• Human Health, Economic, and Environmental Assessment of Onsite Non-Potable Water Reuse Systems for a Large, Mixed-Use Urban Building (2020). This study showcases the use of multiple metrics (quantitative microbial risk assessment, life cycle assessment, and life cycle cost analysis) to evaluate the multiple challenges in NPR systems. The use of multiple metrics also allow for identification of weaknesses in systems that lead to burden shifting.
• Live Cycle Assessment of a Rainwater Harvesting System Compared with AC Condensate Water System (2019). This study modeled the life cycle impacts of rainwater, AC condensate, and combined rainwater and AC condensate collection across potential building configurations in two candidate locations. Results showed that the combined system performed equivalently to the better-performing option for all scenarios considered, with relative benefits of either source water driven by local climate conditions.
• Life Cycle Assessment and Cost Analysis of Distributed Mixed Wastewater and Graywater Treatment for Water Recycling in the Context of an Urban Case Study (2019). This report provides results of EPA's use of life cycle assessment and life cycle cost assessment to evaluate several urban building and district scale decentralized wastewater treatment technologies coupled with on-site, non-potable reuse based on a suite of environmental and cost indicators.
• Energy and Greenhouse Gas Life Cycle Assessment and Cost Analyst of Aerobic and Anaerobic Membrane Bioreactor Systems: Influence of Scale, Population Density, Climate, and Methane Recovery (2018). This study calculated the energy and greenhouse gas life cycle and cost profiles of transitional aerobic and anaerobic membrane bioreactors. Membrane bioreactors represent a promising technology for decentralized wastewater treatment and can produce recycled water to displace potable water.

Collaboration

EPA researchers are committed to active engagement with various partners and stakeholders to ensure that implemented water reuse protect public health. One of these partners, the National Blue Ribbon Commission for Onsite Non-Potable Water Systems (NBRC), is an nationwide group of utilities and state/local public health agencies that are interested in advancing the safe adoption of ONWS. To that end, NBRC has produced several industry guidance documents that incorporate the results of EPA research in this area. Learn more about the NRBC 

Research Publications

• A Guidebook for Developing and Implementing Regulations for Onsite Non-potable Water Systems(2018). This guidebook builds upon this extensive research and provides a specific framework and templates for state and local jurisdictions to use as they craft regulations, adopt policies, and develop and implement local programs for ONWS.

Related Resources

• Water Reuse Action Plan
• Technical Brief: Onsite Non-Potable Water Reuse Research (pdf)
• Webinar Recording: Onsite Non-Potable Water Reuse with Expert Panel Discussion (October 31, 2018)
• Webinar Recording:  Fit-for-Purpose Water Updates and Life Cycle Comparisons of Non-Potable Water Reuse Scenarios (February 24, 2021)
• Water Reuse Research
• 2012 EPA Guidelines for Water Reuse