For fifteen years, one project has defined what water reuse can be. The largest advanced purification system of its kind on the planet, it takes water that was once sent to the ocean and turns it into a drinking supply for close to a million people, and in doing so has become the reference point that utilities from Singapore to Texas study before building their own. But its final expansion is now complete, and the most ambitious chapter of its story may be the one that begins where construction ends: not how big a system can become, but how well it can be run, how much it can still teach, and how far the lessons of one Californian basin can travel.
When the Orange County Water District switched on the Groundwater Replenishment System in 2008, it was not inventing water reuse so much as staking a claim to its future. The District had been purifying wastewater since the 1970s, when Water Factory 21 became one of the first facilities in the world to treat sewage to a quality fit to recharge an aquifer. What the GWRS did was take that pioneering idea and build it at a scale no one had attempted: a system that would grow from 70 to 100 and finally, in 2023, to 130 million gallons a day, recycling every drop of reclaimable flow from its neighbouring sanitation district and turning what was once discharged into the Pacific into a locally controlled drinking water supply for close to a million people.
Now that the GWRS has reached its full build-out, success is measured less by construction milestones and more by long-term performance
Today the GWRS is the largest advanced purification system for potable reuse on the planet, and the reference point against which projects from Singapore to Texas to Australia measure themselves. Its three-step treatment train — microfiltration, reverse osmosis and ultraviolet light with hydrogen peroxide — has become a template, but the more instructive part of the Orange County story is what surrounds the technology: a four-decade partnership between two public agencies, a groundwater basin used as both reservoir and natural barrier, an in-house research programme that few utilities of any size can match, and a community that was brought into the conversation a full decade before the plant came online. Success here was never only an engineering achievement.
That is what makes this an interesting moment to speak with the man now responsible for it. John Kennedy took over as General Manager in early 2024, after more than four decades at the District and immediately after the GWRS reached its final build-out — the point at which the construction era ends and a quieter, harder discipline begins: operating a mature system at peak efficiency, deciding which emerging technologies are worth the investment and which are not, and carrying the institutional knowledge of a generation into the next. In the conversation that follows, John Kennedy explains why the world's flagship reuse system measures success differently now, what its research is uncovering, and why he is convinced that local water reliability is worth paying for.
You took the helm at OCWD shortly after the GWRS reached its final build-out. Succeeding Mike Markus after his three and a half decades at the District is no small handover. What does it mean, in your day-to-day, to lead the world's largest water reuse system when the construction era is essentially behind you, and how does that shift the way you measure success as General Manager?
I worked alongside Mike Markus throughout his tenure as General Manager, so there was a lot of continuity when I stepped into the role. Mike did a great job, and I knew I could rely on my 40 years of experience in the water and civil engineering industry to build upon that momentum while adapting to changing conditions. Now that the GWRS has reached its full build-out, success is measured less by construction milestones and more by long-term performance. It’s about reliability, water quality, operational excellence, and making sure we continue considering new technologies, regulations, and challenges facing the water industry.
I’m also focused on evaluating how we operate the groundwater basin and whether there are opportunities to safely increase annual pumping and storage over time. It’s complex work, but that’s part of making sure OCWD remains forward-looking and prepared for the future.
With the system fully built out, where do you see the next frontier of operational performance and what would you say are the toughest engineering and operational challenges that remain at the GWRS today?
We’re always looking at ways to improve the efficiency and performance of the GWRS through research, emerging technologies and operational optimisation. Our R&D team plays a major role in that effort, whether it’s evaluating new membrane options, treatment processes, chemical changes or ways to operate the system more efficiently. One small change can save you millions of dollars in operating costs.
California's direct potable reuse regulations have been in effect since late 2024, and several utilities, including some of your neighbours, are moving toward DPR. OCWD operates the world's flagship IPR system. Do you see DPR as a future path for OCWD, or is the natural barrier of the groundwater basin a strategic asset you wouldn't trade?
You are correct. Direct Potable Reuse (DPR) doesn’t make sense for OCWD because we have a vast groundwater basin that delivers the GWRS water to our retail agencies. Additionally, the groundwater basin provides another treatment step, helping to ensure the quality of the water always meets federal and state regulations. And finally, and this gets little mention with the project, the low-TDS GWRS water offsets higher TDS water supplies that are used to replenish our basin.
Direct Potable Reuse doesn't make sense for OCWD because we have a vast groundwater basin that delivers GWRS water to our agencies
If a utility leader anywhere in the world came to you today asking which path to take, IPR with environmental buffer, or DPR direct-to-distribution, what would your honest advice be, and what are the conditions that should drive that choice?
Every community is different, and the approach to water reuse depends on the resources, environment, and infrastructure available locally. Communities that don’t have access to a surface water reservoir or groundwater basin may need to pursue more expensive DPR because they don’t have the ability to store water before it enters the drinking water system. In Orange County, we have the advantage of a large groundwater basin, which allows us to replenish highly purified GWRS water for storage, and it eventually becomes part of our service area’s drinking water supply.
OCWD's R&D programme, under Dr Plumlee, has published consistently in leading journals and runs pilots with industry partners such as DuPont, ROTEC, Porifera and others. Few utilities anywhere maintain in-house research at that level. Why has OCWD chosen to invest in research as a core function rather than outsource it, and what has that returned to the District?
For OCWD, it’s been worth the investment. Our staff knows the system and operations better than anyone, and having a top-tier in-house R&D program allows us to test new membranes, new chemicals, different treatment approaches, and operational strategies directly on our facilities by using pilot systems, which are essentially smaller-scale versions of the large purification systems used at the GWRS. That work helps us evaluate promising new technologies and approaches to improve water quality, enhance water recycling and groundwater recharge, and increase efficiency in District operations. The GWRS also serves as a large test bed for others to test emerging technologies coming on the market. We’ve also always tried to collaborate with industry partners and researchers to enhance our operations and share what we learn with the broader industry.
Beyond the GWRS, a recent example is our R&D staff’s ongoing trials of different adsorbents that remove PFAS from drinking water; this work led to a particular adsorbent being selected for the regional full-scale PFAS treatment plants we are constructing in locations where groundwater supplies have been impacted by PFAS. Fortunately, this type of treatment is not necessary for GWRS since RO does an excellent job removing PFAS from purified recycled water.
Looking at the technologies you've been piloting in recent years, from concentrate recovery to next-generation membranes to PFAS treatment, which ones do you believe are closest to being mature enough to change how potable reuse is delivered at scale globally?
While it’s critical that water utilities provide research partnerships to academia and other technology developers, the technologies that are closest to being implemented at scale are typically the innovations offered by mature companies who know the sector’s needs, as well as start-up companies positioning to bring something new commercially. For membrane-based potable reuse like done at OCWD, our R&D has demonstrated that recovery of additional water from reverse osmosis (RO) concentrate is absolutely possible, but it’s a question of whether the investment is worth it in terms of new water produced. For us, that’s still an open question. On the water quality side, our team has also been piloting a promising membrane disinfection alternative – hydrogen peroxide added before ultrafiltration and RO – that could altogether eliminate the production of regulated disinfection byproducts while controlling biofouling as well or maybe even better than chloramine, which is the current approach used across the industry for our type of treatment train to control membrane biofouling.
The GWRS is widely cited as producing water at a lower cost than imported supplies and at a fraction of the energy of seawater desalination. From your perspective as both an engineer and someone who has spent years on the District's financial planning, what is the honest economic case for reuse compared to its main alternatives — and where is that case most fragile?
Recovery of additional water from RO concentrate is absolutely possible - but it's a question of whether the investment is worth it
The economic case for reuse is really tied to long-term local reliability. For OCWD, the cost of GWRS water has consistently remained well below the cost of imported water, while also giving us a dependable local supply that we can manage close to home. The GWRS, with its size, clearly benefits from economies of scale. Additionally, the plant was designed to operate at the same flow rate 24/7, 365 days a year, which also contributes to the low unit costs.
These projects require major upfront investment, which is why grants, low-interest loans and other outside funding are so important to help offset costs for ratepayers. OCWD has been very proactive about securing outside funding through state and federal programs and other sources whenever possible.
From my perspective, local reliability is worth paying for. Imported water from northern California and the Colorado River is becoming more expensive and less predictable, so there’s real value in investing in a sustainable local supply. The most fragile part of the economic case is making sure agencies have access to the funding needed to build and maintain these projects while keeping water affordable for their communities.
The OCWD–OC San partnership has been described as the institutional secret behind the GWRS. Looking at projects elsewhere, in California, in Texas, in Australia, in Singapore, how replicable is that model, and what conditions does a region need before it can even attempt something similar?
The partnership factor has been a challenge for many reuse projects. The relationship between OCWD and OC San has worked because both agencies recognised early on the general benefit of water reuse to the region. Beyond the general benefit, OCWD needed additional water supplies to support groundwater replenishment and strengthen the seawater intrusion barrier, while OC San needed an alternative to building a new ocean outfall for wastewater discharge. Both agencies saw the long-term value of the project and stayed committed to making it successful from the board level through staff.
Successful projects like ours also require strong communication, clear agreements, and regular coordination between both agencies. There are a lot of operational, financial, and planning decisions that have to be worked through together over time. The model can absolutely be replicated, but it requires a true long-term partnership and a willingness from both agencies to work collaboratively through challenges as they arise.
The recent AWWA report puts the US drinking-water investment gap in the trillions, with federal participation at historically low levels. As a utility leader, how do you see the financing architecture for the next generation of reuse projects coming together — and what role should federal programmes like WIFIA, SRF and Title XVI play?
State and federal funding programs like WIFIA, SRF and Title XVI are extremely important and should be maximised by agencies whenever possible. Reuse projects require major upfront investment, and outside funding helps reduce the burden on ratepayers and makes these projects more affordable for communities. Additionally, receiving outside grant funding provides significant positive momentum for reuse projects that can take years to process. That said, OCWD would have still moved forward with GWRS even without that funding because we recognised the need for a reliable long-term local water supply for Orange County. It really comes down to need. Communities are going to have to continue investing in local water supplies for both current and future generations. Funding programs help make those projects more achievable and can accelerate how quickly agencies are able to move forward.
OCWD now runs what is widely regarded as the largest regional PFAS treatment programme in the United States, with mitigation costs projected across multiple decades. Beyond the technical response, what has this experience taught you about how utilities should be sharing the cost burden between ratepayers, polluters and public funding?
One of the biggest challenges with PFAS is that utilities and ratepayers should not be carrying this burden alone. Water agencies did not create these chemicals, so there must be a strong “polluter pays” component. Addressing PFAS in Orange County is estimated to cost approximately $1.8 billion over the next 30 years, which is simply too large for local communities to absorb on their own. That is why OCWD has aggressively pursued both litigation and external funding opportunities.
To date, the District has secured approximately $283 million through outside grants and legal settlements with chemical manufacturers to help offset treatment costs and minimise impacts to ratepayers.
For OCWD, our approach has been an “all-for-one, one-for-all” model among our 19 cities and retail water districts. PFAS impacts are being addressed collectively across the basin, with OCWD partnering closely with local groundwater agencies to help fund and implement treatment projects so the responsibility is shared regionally rather than falling on any one agency alone. This principle also creates economies of scale and a more cohesive regional approach where OCWD can share technical resources, research, operational experience, and communication strategies with its member agencies while working toward the same goal of protecting water quality.
The water sector is openly worried about a workforce cliff, a wave of retirements, hard-to-fill operator and engineering roles, and the loss of institutional knowledge. OCWD has just lived through one of those generational transitions itself. What is working for you in attracting and keeping the people who actually run a system like the GWRS, and what isn't?
A lot of this work takes years of hands-on experience to learn well - replacing that institutional knowledge is not easy
We’ve put a big focus on investing in our employees through ongoing training, professional development, and opportunities to grow within the organisation. These systems are becoming more advanced and technical, so you have to keep developing your workforce over time. We’ve also worked closely with local colleges, trade schools, and organisations with established internship programs, helped create apprentice opportunities, and served as a host site for interns, including in operations. Tours, career fairs, and community outreach have also helped expose students and young professionals to careers in the water industry.
At the same time, one of the biggest challenges is that a lot of this work takes years of hands-on experience to really learn well. Replacing that institutional knowledge is not easy, which is why we place a strong emphasis on mentoring younger staff and succession planning throughout the organisation. I regularly encourage supervisors to think about who is being trained and prepared to step into key roles in the future because maintaining that continuity of knowledge and experience is critical for long-term operations.
The GWRS has been the global benchmark for water reuse for nearly two decades. With projects like Pure Water Southern California, NEWater's next expansions in Singapore, El Paso's direct-potable plant in Texas, and others on the horizon, that benchmark will inevitably move. What do you most want OCWD's contribution to the global reuse story to be ten years from now, and if you were designing the successor of the GWRS from scratch today, what would you do differently?
We want the GWRS to continue serving as a global model for water reuse and help other communities move forward with their own projects. A big part of that has always been to be willing to share what we’ve learned with the rest of the industry. Looking back, I think the phased approach worked very well for us. We also started public outreach early – 10 years before the project even came online – were honest and transparent, invited the community into the process, and built support over time through tours, independent expert review panels and legislative support.
There’s always room for improvement, but I think we did the big things right and have continued learning lessons along the way. Even today, with the system fully built out, we’re still looking at ways to improve the system and squeeze every drop to enhance water supply reliability.
