Direct Potable Reuse Of Water

As water reaources become increasingly scarce in California, attention has turned to ways to make the best use of the water that we have. One such method of stretching our water supply is direct potabte reuse. Direct potable reuse as the introduction of highly treated recycled water either directly into the potable water distribution downstream of a water treatment plant (i.e., pipe-to-pipe), or into a raw water supply immediately upstream of a water treatment plant.

What follows are key points from the paper Regulatory Aspects of 'Direct Potable Reuse In California' by James Crook, National Water Research Institute, April, 2010.

There are many Issues related to direct potable reuse that need to be resolved before adequate regulations can be crafted. Some of the issues are interrelated (e.g., multiple barriers, retention time, monitoring), and means to resolve any specific issue should consider the positive or negative effect it may have on the resolution of other issues. Key issues that should be addressed include the following:

1. Definition of direct potable reuse. There needs to be a dear distinction between what constitutes direct potable reuse (DPR) versus indirect potable muse (IPR). Although direct potable reuse is commonly defined as the introduction of recycled water directly into a potable water distribution system downstream of a water treatment plant, there are other definitions that identify other schemes that may also be considered as direct potable reuse. A standard, inclusive definition of direct potable reuse is needed if the regulatory agencies are to approve direct potable reuse, as different schemes would be subject to differing regulatory requirements.
2. Compensation for loss of an environmental buffer The California Department of Public Health (CDPH) embraces the concept of an envinronmental buffer for indirect potable reuse projects as one of the multiple barriers that provides some degree of additional recycled water quality improvement and provides time to take corrective action in the event that monitoring indicates that the product water does not meet all required constituent limits. Means to compensate for the loss of an environmental buffer will likely be required if direct potable reuse is to become a reality Such means could include additional multiple barriers for microbial and chemical constituents of concern, improvements in currently-used treatment processes, Incorporation of new treatment processes into the treatment train, enhanced monitoring methodologies and/or short-term storage of product water that would provide time for monitoring results to be determined prior, to use as a potable supply.
3. Multiple barriers. The multiple barrier-approach undoubtedly would be required to ensure that all regulated and unregulated constituents of concern are reduced to acceptable levels in the product water. The number, type, and reliability of treatment processes necessary to ensure that constituents of concern are reduced to acceptable levels in the product water would need to be determined. While several treatment processes have been demonstrated to reduce the concentrations of these constituents to acceptable levels, the removal of unknown constituents that may be of health concern is not as clearly defined. It may be necessary to provide more robust multiple treatment barriers than those currently used at existing IPR projects to gain regulatory approval of a direct potable reuse project.
4. Dilution. The current CDPH draft groundwater recharge regulations for IPR require dilution by specifying maximum recycled water contributions. The dilution requirement may be waived over time upon demonstration that total organic carbon in the recycled water does not exceed 0.5 mg/L and that all water quality requirements can reliably be met.
5. Constituents of concern and monitoring. There is a need to identify constituents of concern that should be monitored for either directly or indirectly via the use of surrogates. Real-time online monitoring is desirable, but may not be achievable for many constituents/parameters with existing technology. COPH will have to determine whether existing treatment process efficiencies for constituent reduction/removal and monitoring methodologies are adequate to eliminate the need for an environmental buffer and retention time after treatment of the recycled water. Improvement in treatment process removal efficiencies and/or monitoring methods may be necessary to enable the consideration of direct potable reuse in Califomia.
6. Assessment of health risks. The CDPH Policy Memo 97-005 (Policy Guidance for Direct Domestic Use of Extremely Impaired Sources) requires an evaluation of the risks of failure of a proposed treatment system and an assessment of potential health risks with a failure. Policy Memo 97-005 states that the health risk assessment must take into account the human health risks associated with exposure to insufficiently treated water considering The risks of disease from microbial organisms and the risks of acute and chronic affects from chemical contaminants. Clarification is needed from CDPH as to what such a health risk assessment would entail.
7. Independent Advisory Panels. CDPH now requires a scientific peer review of certain IPR projects involving groundwater recharge by independent advisory panels. While it is not known if CDPH would require similar panels of experts for direct potable reuse projects, such a requirement would appear to be likely.
8. Applicibility of existing CDPH regulations. CDPH's permit procedures and compliance with source water assessment, surface water regulations, drinking water standards, and possibly Policy Memo 97-005 Policy Guidance for Direct Domestic Use of Extremely Impaired Sources) do not specifically address direct potable reuse. Their applicability to direct potable reuse projects needs to be evaluated.
9. Regulatory responsibity. The various regulatory agencies may need to consider clarification of the point at which the water makes the transition from Water Code to Health and Safety Code authority. This transition point defines the beneficial use of the recycled water.
10. Development of a communication management system among agencies. A communication system must be developed to enable all operating, and regulatory agencies involved in a direct potable reuse project to work together to avoid the distribution of unsafe drinking water.