Why Adopt the Risk-Based Framework for On-site Non-potable Water Systems
The Risk-Based Framework (RBF) is an internationally accepted water quality treatment standard that is more protective of public health than current Environmental Protection Agency (EPA) standards for conventional drinking water and resource recovery (i.e. “waste”water) treatment systems. The RBF is suitable for designing, operating and maintaining on-site non-potable water systems (ONWS).
This document summarizes the “Risk-Based Framework for the Development of Public Health Guidance for Decentralized Non-Potable Water Systems” (RBF guidance) for the public. It was developed and published by the Water Environment & Research Foundation.
What’s an “On-site Non-potable Water
On-site: Treatment occurs where water will be re-used.
Non-potable: We can’t drink it, but it’s great for many other uses!
Water: That substance that we’re all mostly made of and that we can’t live without for long.
System: The pipes, tanks, pumps, and equipment that stores, treats and moves water.
Put all these words together and ONWS systems covered in the Risk-Based Framework include:
- Condensate (water from the air) harvesting
- Rainwater harvesting
- Stormwater harvesting
- Foundation water
- Reuse of water from fixtures without fecal matter or urine (e.g. sink, tub/shower, clothes washers when washing clothes)
- Reuse of water from fixtures with fecal matter or urine (e.g. toilet, urinal, clothes washer when washing diapers)
Why do we need the Risk-Based Framework?
Even though ONWS provide solutions for some of the nation’s most pressing problems, national standards for planning, designing, permitting and operating ONWS don’t exist. Aside from the benefits that will accrue once the these systems are widely built, first there are many additional benefits of adopting the RBF.
How does the RBF protect public health over other frameworks?
Many permitting agencies develop performance-based standards (i.e. standards that require an outcome but don’t explicitly define how that outcome is achieved). For water reuse, though, they do this by adapting existing water quality standards for recreation or for centralized municipal wastewater reuse systems. Unfortunately, existing regulations do not fully consider and address the differences in scales, incoming water quality, or outgoing water quality needed for any given end use.
How does the RBF protect public health over other frameworks?
The RBF “provides a flexible framework that can be 1) adapted to new water sources and end uses and 2) modified based on experience gained in operating decentralized non-potable water systems” 3.
How does the RBF account for exposure risk?
Experts refined the RBF based on science and their own experience with performance of these systems. They wanted to ensure that the water quality is right for the risk associated with the end use. They applied a methodology used by the World Health Organization (i.e. Quantitative Microbial Risk Assessment) to “estimate the potential risks to human health resulting from exposures to microbial hazards” (i.e. “pathogens”, which are viruses, bacteria, and protozoa that could make people ill).
Three risk management categories consider
1) the number of people served by the ONWS, 2) the pathogen levels of non-potable water sources, 3) end uses and their potential for human exposure, and 4) the complexity of the treatment mechanisms to operate and maintain.
“Log reduction targets” (LRTs) define the degree to which pathogens must be reduced for a variety of on-site-generated waters and their end uses. These LRTs are based on the number of pathogens over time and the potential for pathogens to occur now and then.
Agencies permitting ONWS may choose between requiring conservative and less conservative LRTs, which are specific to each water source, end use, and pathogen type (i.e. viruses, protozoa, or bacteria).
How does the RBF assure proper design of ONWS?
Design guidance for a variety of technologies is provided in the RBF guidance and a few example projects show how to use the RBF guidance to design treatment trains.
The RBF is based on an already established and accepted design method. As for other systems, designers know how many pathogens can be reduced by specific treatment systems. Designers define how to operate the systems and include control points to measure performance along the way. The values they measure are called “log reduction values” (LRV). Designers apply treatment processes in a specific order (i.e. “treatment train”) to achieve the required LRT required by regulation. Then, they monitor to measure and confirm the actual LRVs.
How does the RBF assure proper operations and maintenance of ONWS?
RBF guidance is provided for identifying and establishing the Responsible Management Entity (RME) who is responsible for operations and maintenance of approved ONWS. The RME must carefully consider how operations and maintenance will be financed and provide this information to regulators.
Performance monitoring may consist of validation testing, field verification, and/or continuous verification monitoring. Which method depends on the 1) risk management category (described above in “How does the RBF account for exposure risk?”), 2) pathogens that are present and 3) the kinds of equipment incorporated into the design.
Data is collected from each of these methods and included in a commissioning report submitted to the appropriate permitting agency for final permit approval.
Isn’t there a risk that pathogens will emerge and/or grow back when treated water is stored and distributed?
Yes. “The largest recognized cause of waterborne risk from drinking waters in the United States is premise-plumbing growth of Legionella”. Existing centralized wastewater treatment plants manage pathogens very well and lessons learned there can be applied to ONWS. The RBF guidance details what pathogens are concerning and how to prevent their growth while storing and distributing treated reused water, including for fire suppression.
How will a permitting authority confirm ONWS meet regulatory requirements for initial and final approval?
The permit application report (PAR) is the primary tool for regulators to assess whether the proposed design will achieve the log reduction targets (LRTs) and meet other regulatory requirements. The RBF guidance provides a template for both the draft PAR and the final PAR, which at minimum for complex systems should include 1) information on “responsible management entity, 2) project overview, 3) relevant regulations, 4) water source, 5) treatment processes, 6) reliability, 7) water uses, 8) cross-connection control, 9) water quality and log reduction value monitoring, 10) facility commissioning plan, 11) operation and maintenance plan, and 12) provisions for water quality exceedances, power outages, spills and other emergencies” 3.
RBF guidance recommends that a “trained group of professionals should review and approve PARs and other reports required for project approval. The regulating jurisdiction or a third party authorized by the jurisdiction should undertake this review. Reviewers should have knowledge of cross-connection control practices, environmental health, on-site wastewater systems, and water treatment design and operation. It may be necessary to have a Registered Professional Engineer (PE) review a submittal prepared by another Registered Professional Engineer.”
Recode is a nonprofit that works to insure clean water is available for people and the environment. Recode speeds the use of practices that are currently too expensive, are misunderstood by the public, and/or aren’t allowed by codes. Access to water continues to decline in recent years, so recode focuses on fostering resilient communities.
“Risk-Based Framework for the Development of Public Health Guidance for Decentralized Non-Potable Water Systems” developed and published by the Water Environment & Research Foundation.