Of Dreamliners and Drinking Water

Michael Kiparsky and Christian Binz

As we have written previously, potable water reuse (recycling water to augment water supplies) is a promising way to diversify urban water supply portfolios. Direct potable water reuse (DPR), the injection of highly purified wastewater into drinking water systems, is among the newest, and most controversial, methods for augmenting water supplies.

DPR is garnering increasing interest, but does not come without risks.

In a new article, several of us examine the notion that emerging regulation of DPR may lack sufficient attention to catastrophic risks with low probabilities of occurrence, but high consequences. In other complex engineered systems, such black swan occurrences have emerged in seemingly “failsafe” systems with disastrous results. The Hindenberg, Titanic, Fukushima, and Deepwater Horizon are iconic examples.

The DPR industry is subject to similar types of risk, such as those related to an unintentional spill of pathogens into a city’s drinking water supplies. We thus argue that proponents of DPR could benefit from broadening their risk management, by acting to 1) proactively develop a safety culture in utilities employing DPR, and 2) establish an effective industry-wide auditing organization. Developing independent oversight for DPR operation could ensure that quality and management requirements are set and enforced, and that any system failures or “near misses” are investigated and adequately responded to.

Image credit: Hazen and Sawyer

Two types of risk

In its simplest definition, risk is the probability of an event occurring times the consequences of that event. However, risk manifests in very different ways, and an important conceptual distinction can be made between risks with high probability and low consequences (e.g., flight delays), and low probability risks with high consequences’ (e.g., airplane crashes). The latter (“LPHC risks”), include catastrophic, large-scale events with negative externalities, and resist market-like solutions such as compensation for risk. LPHC risks are more difficult to perceive accurately, let alone manage effectively. LPHC risks are often only implicitly considered, if considered at all, by regulators and managers.

Lessons from other industries

Seeking lessons on how to manage LPHC risk, we looked to the risk management literature and examined the history of three other industries: aviation, offshore oil, and nuclear. Each experienced catastrophic failures, and attempted to manage them at an industry level.

What is missing

Recent framework documents and draft regulations for DPR (mostly from California, which is most advanced in developing regulations) are forward looking, but show key gaps in preparing for human-induced system failures. Recent California legislation creates a pathway towards the regulation of DPR (Cal. Water Code §§13,560–70), mandating two reports from external panels. The advisory group report contains recommendations that explicitly focus on the human dimension of this complex technology. For example, the report recommends that Advanced Water Treatment Facility operators obtain special training and certification. While these recommendations are clearly related to elements of safety culture, the report does not seek to codify broader recommendations on the establishment of an industry-wide safety culture.

Further, independent oversight matters for sustaining compliance with basic safety standards. A number of governance forms have emerged in other sectors that could be adapted to DPR. In aviation, an industry-wide organization was created that assesses all accidents and ‘near misses’ and proposes safety enhancements on a voluntary basis. In the nuclear industry, mechanisms exist that facilitate knowledge transfer about safety issues and creates substantial peer pressure among plant operators to maintain the highest possible safety standards. Important elements of their governance include independence, transparency, oversight capacity and accountability.


It is in the interest of the emerging DPR industry to avoid its own Fukushima event. A drinking water system mishap could have high “signal potential,” and could easily set back public acceptance of a technology that is already struggling against consumers’ psychological barriers (the “yuck factor”), a lack of broader societal legitimacy, and the industry’s general challenges with innovation. The industry could proactively address LPHC risks upfront, by working to develop effective plans for establishing utility safety cultures and effective oversight. Examples from the aviation, nuclear, and oil industry show that such interventions do not necessarily require new layers of regulation, but can be designed in efficient, participatory, and even voluntary ways.

While potable reuse may become an increasingly important part of water supplies in many regions, it is not yet viewed as an irreplaceable element of the urban water system. With public support still fragile, the industry may be particularly vulnerable to public opposition arising from a high-profile catastrophic failure. Avoiding, or preparing for, catastrophic failure is important for DPR’s credibility and mid- to long-term viability. We argue that creating safety-enabling systems is actually in the DPR industry’s self-interest. If an effective LPHC risk management system were established, technology proponents could convey the powerful message that “we safeguard your drinking water using the same methods that keep you safe when you fly on an airplane.” The positive effect of such a message on DPR’s social legitimacy could easily justify the effort necessary to be able to deliver it with confidence.


This post is based on a newly published article, currently available online:

Christian Binz, Noosha Bronte Razavian, and Michael Kiparsky. 2017. “Of Dreamliners and Drinking Water: Developing Risk Regulation and a Safety Culture for Direct Potable Reuse.” Water Resources Management, doi:10.1007/s11269-017-1824-1

Reader Comments

4 Replies to “Of Dreamliners and Drinking Water”

  1. “What is missing” are the High Probability High Consequences (HPHC) of failing to eliminate or treat pharmaceutical and other chemical human waste products from “toilet to tap” recycling. The euphemism, “Direct Potable Reuse”(DPR), purposely avoids the word “toilet” as a primary source of reused water for more than psychological reasons.

    DPR wastewater treatment generally is limited to ultraviolet and enhanced filtration methods that do not remove toxic chemicals that are passed into human waste through pharmaceutical products, contaminated drinking water, chemically treated food products and other sources.

    By avoiding consideration of contaminants in human waste, and whether they are fully eliminated or treated for recycled drinking water, catastrophic risks to human health will occur on a constant, rather than infrequent, basis. No slogan or public relations effort can change such High Probability High Consequences.

    1. Jai Rho –

      Thank you for this comment.

      Your characterization of the risks are not in line with those of the National Research Council and other review bodies, which have reported that DPR can reliably treat wastewater to high standards, and indeed to standards higher than many source waters. You might review the NRC’s assessment (reference below) as one example for more details on treatment processes and risk assessment.

      Your comments do serve to illustrate the psychological power of the “yuck factor” and how it can raise significant opposition to DPR projects. Our previous post on this topic discussed the need for broader efforts to generate societal legitimacy for DPR, if it is to be deployed as part of water supply portfolios.

      Mike Kiparsky

      National Research Council (US). Committee on the Assessment of Water Reuse as an Approach for Meeting Future Water Supply Needs. In Water Reuse: Potential for Expanding the Nation’s Water Supply Through Reuse of Municipal Wastewater; National Academies Press, 2012.

      1. The use off recycled water for crops consumed raw is another area where there is an unknown but potentially high consequence public health risk. If the document cited from NAS/NRC is the one I also looked at, they panned antibiotic resistant genes (ARGs) as an essentially non-issue? The State Water Resources Control Board also tends to ignore discussions on ARGs and notes that the Anderson Expert Panel (2010) did not consider antibiotic resistance bacteria (ARB) as an issue. Interestingly, it seems that the Anderson Panel was not qualified to make such pronouncements on antibiotic resistance and later admitted such. Nonetheless, the State of California continues to put forward the Anderson Panel’s statement. This type of action merely enhances the case for LPHC events as those who should be more responsible seem to get the normative and pragmatic agendas confused.

        The State of California, last time I spoke to the SWRCB, had no training of plant operators in the areas of ARBs or ARGs. Interestingly, when we test recycled water at the plant when first released, it tests low in bacterial count to ND with MPN single indicator tests. If we parallel test with disk diffusion (on Mueller-Hinton) for antibiotic resistance at the same time and run these tests, we are finding that same water high with counts of ARBs, some testing at resistance to 11 of the 12 antibiotics in our Kirby-Bauer. If we then move down the purple pipe to the POU, the MPN counts are now off the charts. Thus, we opine that resuscitation or shedding biofilms may be the cause. WERF found the rebloom of VBNC to be an issue with wastewater byproducts, thus raisin worrisome questions about the validity of the standard test. Harwood and Rose also have raised serious questions about the validity of the single indicator test, especially at sample sizes typically used.

        If one looks at the Calif Supreme Court Case Hartwell, it appears that unless there are numeric standards, there is limited enforcement capacity. Since many of the CECs, including ARBs and ARGs do not have numeric standards, this absence may merely add to the level of risk. It is well documented that tertiary level treatment does not stop ARGs.

        There are solutions for the above but that seems to command a grasp of political circumspection that seems to be eluding the discussion along with the topic of clientele capture amongst the regulatory community.

        Dr Edo McGowan

  2. Michael – would you and Legal Planet allow us to move your column to the CWEA blog as well so you can address water/wastewater operators and managers directly?

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About Michael

Michael Kiparsky

Michael Kiparsky is Director of the Wheeler Water Institute at CLEE at Berkeley Law.…

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