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Debunking ‘Toilet to Tap’, with Mike Markus

With climate change threatening freshwater sources, water demand across the globe is likely to increase by 20 – 30% between now and 2050. In this episode, we’re looking at two promising solutions to create clean drinking water from surprising places: our sewers and oceans.

We speak with General Manager of the Orange County Water District, Mike Markus, about debunking the “toilet to tap” fear and how turning our wastewater into clean drinking water can be a closed-loop solution to mounting water scarcity. We also hear from Dr. William Tarpeh about new research at Stanford University that could make desalination a more viable solution; one that’s less costly and better for the environment.

Guest Bios

Mike Markus
Mike Markus

Michael (Mike) R. Markus is the general manager of the Orange County Water District (OCWD; the District), which manages the Orange County Groundwater Basin that supplies water to more than 2.5 million people in north and central Orange County, Calif. With more than 40 years of experience, Mike is well known for his expertise in large project implementation and water resource management. In September 2007, he became only the sixth general manager in the District’s history.

During his 33-year career at the District, Mike was responsible for managing the implementation of the $480 million Groundwater Replenishment System (GWRS) program. This project is the largest potable reuse project in the world and has won many awards including the 2008 Stockholm Industry Water Award, 2009 ASCE Outstanding Civil Engineering Achievement Award, 2014 U.S. Water Prize and the 2014 Lee Kuan Yew Prize. In 2015, Mike oversaw the completion of the 30 MGD GWRS Initial Expansion. The expansion brought the total production capacity of the GWRS to 100 MGD of high-quality water, which is enough to serve 850,000 people annually.

Mike was named the 2017 Pioneer in Groundwater by the Environmental & Water Resources Institute, one of the Top 25 Industry Leaders of 2014 by Water & Wastewater International, he received the international 2009 Säid Khoury Award for Engineering Construction Excellence, the 2007 American Society of Civil Engineers’ Government Engineer of the Year award, and he was one of the Top 25 Newsmakers of 2007 by the Engineering News-Record.

Mike currently serves on the board of directors of the Water Research Foundation, the National Water Research Institute, American Water Works Association and the California Section of the WateReuse Association. He obtained a Bachelor of Science degree in civil engineering from California State Polytechnic University, Pomona and a Master of Science degree in civil engineering from the University of Southern California. He is also a registered civil engineer in the state of California.


Dr. William TarpehDr. William Tarpeh

Dr. William Tarpeh is an assistant professor of chemical engineering at Stanford University. The Tarpeh Lab develops and evaluates novel approaches to resource recovery from “waste” waters at several synergistic scales: molecular mechanisms of chemical transport and transformation; novel unit processes that increase resource efficiency; and systems-level assessments that identify optimization opportunities. Will completed his B.S. in chemical engineering at Stanford and his M.S. and Ph.D. in environmental engineering at UC Berkeley, supported by an NSF Graduate Research Fellowship, Ford Foundation Predoctoral Fellowship, and a UC Berkeley Chancellor’s Fellowship. He conducted postdoctoral training at University of Michigan in environmental engineering. Will is a member of the Bouchet Honor Society, NBCBLK’s “28 Under 28” African-American Innovators, and Forbes’ “30 Under 30” 2019 Science List. Tarpeh’s CV is available here.


Further Reading

OCWD Facilities Pictures



@OCWDWaterNews – Orange County Water District

@TarpehDiem – Dr. William Tarpeh


@OCWD – Orange County Water District


OCWater District


Orange County Water District

Photo Credit

Mike Markus – Submitted
William Tarpeh – Submitted
OCWD Facilities photos – Submitted

Full Transcript

Mike Markus: We consider wastewater a resource, not a waste. By the time it’s gone through our treatment process, it’s nearly distilled water. with climate change and everything else, so sources of supply are very. variable moving forward into the, in, into the future. 

So it’s, it’s really up to us to develop these local supplies,

(Theme Music) 

Jay: We need water. With a growing population, climate change and more humans turning on the taps, our need for water over the next three decades is projected to increase up to 30%. What if I told you that one solution starts in our sewers? 

I’m Jay Famiglietti on this episode of What About Water? We’re adding wastewater to the recycling stream, going from toilet to tap.

Mike Markus is the general manager of the Orange County Water District. He’s worked there for 33 years and he manages this incredible water transformation. I got to know Mike, when I was at UC Irvine, where I became a huge fan of the work that he was doing. We’ve reached him in Fountain Valley, California. Mike welcome to What About Water? 

Mike Markus: Thank you very much, Jay. It’s a pleasure to be with you this morning, 

Jay: So great to have you, so great to see you again.

Can’t wait for our chance to get down to Orange County and tour that amazing facility. Um, I don’t know if you remember Mike, but I used to tell people, “You know, it’s like Disneyland. You should put the groundwater replenishment system on your, like on your tour of Southern California.”

This place is so cool. So, let’s talk about that. What aspects of the water crisis, what led you to develop this facility? And specifically I’m talking about the groundwater replenishment system. 

Mike Markus: Yeah, well actually, We down here in Southern California, for those that may not be aware, we live in a desert.

We only get about 13 inches of rain, per year. And, uh, what the Orange County Water District does is manage a very large groundwater basin in central and Northern orange county. So it’s up to us to find additional supplies, sources of water, to replenish the groundwater basin. And we can’t rely on mother nature.

Uh, to do that. So we have to find additional sources and that’s why we turn to recycled water. And our board was very visionary in the mid nineties to identify this and to see treating wastewater to a very high degree, and using that treated wastewater is a source of supply for the groundwater basin. And so that was kind of the genesis of the development of the project. 

Jay: Yeah, so, you know, the usual challenges that Southern California faces: Growing population, lots of people, changing climate, not very much rainfall to begin with and, and all of these issues with not as much snow, that’s a huge problem. So when you say wastewater, where exactly is this water coming from? 

Mike: Well, it actually comes from our neighbor next door, the Orange County Sanitation District. And the Orange County Sanitation District treats all of the municipal and domestic wastewater in Central and Northern Orange County, which serves about 2.5 million people.

So they take the wastewater and they treat it. So they go through it through a primary and secondary type treatment process, which makes the wastewater safe enough to discharge into the ocean. But rather than discharging it into the ocean, we intercept that water after it’s been treated. So, as you mentioned before, we consider wastewater a resource, not a waste.

We take that wastewater, uh, secondary treated, and then we run it through an advanced purification process consisting of micro-filtration, reverse osmosis and advanced oxidation. By the time it’s gone through our treatment process, it’s nearly distilled water. In fact, uh, the end of the tours is as you well know, we give people a taste of the water.

But, we then take that highly purified water and we put it back into the ground. So we put it back into the groundwater basin and, and then the retail water agencies in the area pump it out of the groundwater basin and goes directly into their distribution system, serving their customers.

Jay: That’s pretty amazing. So what’s the capacity these days of the groundwater replenishment system? 

Mike Markus: Well, the current capacity is 100 million gallons per day. And that’s enough water to provide 850,000 people per year. We started out at 70 million gallons per day.

So, uh, we actually started the project back in the mid nineties and we were pilot testing the technologies at that point in time. In the mid nineties, microfiltration hadn’t been used on wastewater. It had been used primarily on surface water as treatment. Uh, so we pilot tested, and wanted to make sure it worked on wastewater.

And then the project evolved in the early two thousands, we decided to move forward with the project. And our first phase went into operation in January of 2008, at a capacity of 70 million gallons per day, with the ability to expand it ultimately to 130 million gallons. We’ve always been saying kind of the first quarter of 2023 we’ll be at our ultimate capacity of 130 million gallons per day, which will be enough water for a million people. 

Jay: Is simply amazing Mike. It’s so great that you’ve been able to increase the capacity like that. So if I were to drop by would I be seeing active construction? I remember, you know, this place, just to describe it to people – and we’ll put some pictures on the website – it is like squeaky clean. It looks so futuristic. I used to also say, so in addition to telling people, you should put it on your, you know, when you’re touring Disneyland and like Universal Studios, you got to go to the Groundwater Replenishment System. I also used to say this place looks like a set for like a James Bond movie.

It’s so futuristic. Is it still like that? Or just getting bigger. 

Mike: It is, it’s really cool. And You’re right. Movie studios have kind of looked around to utilize the facility. And we’ve actually had a couple movies shot here on our campus, but it still is that way. 

We made sure that through these final expansions, we’re using the same type of equipment. So it all looks the same from an operational point of view. It’s all the same. So it’s obviously, yes, it still has that futuristic look and uh, yes, you will see some construction going on if you were to visit us in the coming weeks. 

Jay: I might drop in on you.

Mike: Yeah, you should. We’d love it.

Jay: Um, this all sounds great. Can you put it into perspective in terms of costs? Maybe compare it to, you know, readily available water from metropolitan (met) water district or, you know, desalination, which I want to ask you about later.

Mike: For us, we’re able to produce the water, at an equivalent cost of imported water. So imported water, for those that don’t know in California, Southern California, we rely primarily on water outside of Southern California. So the metropolitan water district of Southern California brings water in from the Colorado River in Northern California. But with climate change and everything else, those sources of supply are very variable moving forward into the future. 

So it’s really up to us to develop these local supplies. The cost of groundwater I should say is about half the cost of met water. So it’s very important for us to find sources of supply so we can continue to utilize the groundwater basin.

As far as the cost of the recycled water, it’s right now equivalent to the cost of met water. And our costs will continue to be lowered as met has its challenges, costs are going to go higher and ours will remain a bit flatter. So we have a more sustainable source of supply uh, certainly And one that over time will actually cost lower than imported water.

Now when you compare that to desalinated water, desalinated water is right now about two and a half times what met water is. It probably is the most expensive supply that would be available. Now it is available and obviously we have an ocean right next to us, we’re, uh, we’re down here along the coast. But at the current time, you know, we always say we should conserve first, recycle next. And ultimately, if we ever need any additional water supply, we do have the ocean, we have the technology, but it is the most costly. 

Jay: You know, I think that’s really an important point, the idea of conservation first and decreasing demand rather than trying to increase supply. So, you know, it’s a challenge to get people to do that. But you mentioned the ocean, and I wanted to just drill down a little bit on whether you’re still using the groundwater replenishment system water as a barrier to seawater intrusion. 

Mike: We are. And back in the mid seventies, started seeing the, uh, sea water, come into the groundwater basin.

So we’re a coastal aquifer, we’re connected to the ocean. And as the seawater started coming in, we feared that it would ultimately contaminate the groundwater basin. And so in the late seventies, we built a seawater barrier along the coast, about five miles in-land. And we started injecting highly treated wastewater at that time.

In fact, we had a facility here onsite called Water Factory 21. And Water Factory 21 was the first facility in the world to use reverse osmosis to treat wastewater. So we’ve been using that technology for a long time, using reverse osmosis, take that water and inject into the ground and form a barrier to keep the seawater from coming inland. So right now, about 20% of the water that we produce goes injected into the barrier. And the other 80% is in a pipeline that we built from Fountain Valley to Anaheim, which is about 14 miles up to our recharge facilities.

So that water then goes into these big like lakes, they’re actually recharge ponds, and that water naturally filters back down into the groundwater basin giving us that additional supply of water. 

Jay: So I want to sort of paint a visual picture. So it sounds like you are taking about 25% of that water and actually building an underground wall right along the coast, an underground barrier wall of water that’s keeping the seawater out. Right? 

Mike: Absolutely correct.

Jay: So, so that’s, that’s cool. And then you’ve got a pipeline that’s basically going up to near like the Los Angeles Angels baseball stadium right up. It’s up, it’s up there. 

Mike: I still like to refer to them as the Anaheim Angels.

Jay: Anaheim Angels. I agree. I just wanted to sound like I knew what I was talking about, but yeah.

So it’s over near Angel Stadium and you’re injecting it into the aquifer and then it’s kind of like, when you go to a nice restaurant and there’s a waiter with a pitcher and he’s kind of standing near the table, he’s going to fill up your glass. If it gets too low, he’s going to fill it up. Right? The waiter’s going to fill up the glass. And that’s sort of how I see the Groundwater Replenishment System, you know, you talk about like, the lower level, you know, the upper level, and so when it gets too low, we should pour in more water. Is that, is that accurate? 

Mike: That is absolutely accurate. In fact, we don’t even wait for the glass to get low. We just continually pour water in, which allows us to maintain a higher amount of water that can be taken out. The more we put in, the more can be pumped out. And as I mentioned before, the economics are such that groundwater will always be cheaper than imported water. 

Jay: So very cool. So you’re like a high-end restaurant, that’s always keeping the glass always keeping the glass full. 

Mike Markus: We like to think so. 

Jay: That’s pretty amazing. So let’s talk about scaling this up and you know, the source of this water is human waste.

And yet here we are in California, like the work that I do is global and you look over the world and you look at these huge agricultural regions that use so much water. Is this sort of recycling, can it help large scale agriculture? Or are we really talking about cities and municipal regions?

Mike: You know, I, I think Jay we’re mainly talking about cities and municipal regions.

I mean, when you go into those agricultural areas in the California Central Valley you have a very limited population. So they’re not generating much, much wastewater. 

Jay: Yeah. 

Mike: Uh, we, we have the ability here being highly urbanized to have a very large source of, uh, supply that’s being treated by the sanitation district.

And that allows us to do the type of recycling that we’re doing. We’re also blessed with a groundwater basin. If we didn’t have that groundwater basin we would not be able to do the amount of recycling that we’re doing. So that’s the other thing. I mean, we were probably best positioned to do this project on this scale because we have the ability to then take the water and put it somewhere, put it in a groundwater basin.

Or if we didn’t have a groundwater basin, we could have put it into a reservoir. But we had the groundwater basin and that’s, that’s what allowed us to build as large a facility as we have. 

Jay: You know, we need to talk about the elephant in the room, which is the “yuck factor.”

And you know, people refer to this as “toilet to tap” and a lot of people, you know, frankly are just grossed out by it. How’d you get around that? 

Mike: Yeah, we have a hashtag #getoverit. But to answer your question directly, that was a big concern for us.

I mean, when we were looking at this project, I mentioned before we started in the early two thousands. And at that time there were projects in Southern California that were trying to do the same thing they were trying to do what we’ll call indirect potable reuse projects. 

A very large one down in San Diego. There was also a couple, uh, up here in LA and all three of them never got off the ground. Because they became politicized, I might say. And people use that terminology that, “Hey, these water districts are forcing you to take water that you’re flushing down the toilet.”

So our board – and I give them a lot of credit, they were quite visionary – when they first met to develop the project, it was 1997. I was there, I remember. Instead of talking about hiring an engineering firm or, you know, any other type of consultant, they said we need to hire an outreach consultant. And that was the first consultant that we hired.

What we did is we did focus groups. We did polling, we found out what the issues are, what the questions were. And then we developed the talking points to be able to answer those questions. And then we went out first to the people that were going to use the water. So we went out to our 19 retail water agencies and got letters of support from all of them.

And then we work the local, state and federal elected officials and we built kind of this political coalition, if you will. We went to the environmental communities. So Coastkeepers, Surf Riders, Sierra Club, all these environmental [groups], uh, they jumped right on board and supported the project.

Health and medical was extremely important also. We had a, uh, a letter from a doctor from the Center for Disease Control, the CDC down in Atlanta, Georgia. She wrote a letter of support early on to the project and that resonated quite well.

So we built this coalition and then we went out and we spread the word. We evangelized. We had the consultant develop what we called a speakers bureau. And we went out and we talked to different civic organizations, chambers of commerce, other different organizations and explained exactly what it was that we were going to do. 

Jay: What were some of those talking points? What were you telling people? 

Mike Markus: Well, we were talking about water supply. We were talking about the safety of the process, using the reverse osmosis and how we had been doing that since the late seventies. We showed the need. You know, we had to have a need as to why we were doing it, the technology behind it. 

I think one thing also that was very effective is when we were delivering these, these talks to these different civic organizations, we had our own staff giving those presentations. We didn’t have the consultants and their fancy Italian suits running out and talking to people.

They took engineers like myself, who are not trained in public speaking by the way. Uh, and they put us in front of people and had us explain the process. And I think what happened, Jay was we got a tremendous amount of public trust, in doing that. 

And that helped us out tremendously. As a result, we had no public opposition to the project. Luckily now we have the ability also to, to give tours of an existing facility. So we take all sorts of groups: university students from some of the local universities, we give monthly public tours, any group that wants a tour of the facility, we will give a tour of the facility. 

We also have a virtual tour. I’ll give a plug. If you go to our website, I give a probably about a half hour forty-five minute virtual tour of the facility and we need to educate people.

We, as a water community, do a terrible job of educating the public. People turn on the faucet, the water comes out, they have no idea where that water comes from – for the most part – but all of the infrastructure behind that and just what it takes to bring water to their homes. 

Jay: It’s magic. I thought it was magic. I thought you turned on the tap and it magically appeared, right? So I want to loop back on something. You’ve mentioned reverse osmosis, a few times. Can you explain what this process is? 

Mike: Yeah. Reverse Osmosis (RO) is you’re basically taking a thin plastic, a thin film, and through high pressure, you’re forcing the water molecules through that semi permeable plastic membrane, we’ll call it. What the reverse osmosis very effectively does is it – I always call it the workhorse of the treatment process – because it removes the dissolved minerals, the viruses and the pharmaceuticals out of the water.

So it takes out most of the contaminants. There are some low weight molecular organics that get through the RO, but our final step, Advanced Oxidation, destroys those low weight molecular organics. 

Jay: Okay. Very, very cool. Yeah. So this is the same stuff that’s used for desalination, right? So we’ve been calling it RO, reverse osmosis. You’re pushing water through a membrane or a very, very fine, almost a filter. And the stuff that’s bigger than the holes in the filter gets left behind.

Mike: Yeah, that’s exactly right. And the reason our process is less costly than say seawater desalination is because of the total dissolved solids in the waters. So our water is less saline, let’s say, it has less mineral salts and minerals. Seawater has about 35 times the amount of these minerals than the wastewater does.

So it takes us less energy to force that water through the membranes. With seawater, it takes a lot more pressure. And that’s where the cost really is, is in the energy. 

Jay: I know you’re expanding. I also know that other places want to follow your lead. Who else is doing this kind of groundwater replacement? 

Mike Markus: You know, probably the best example is the city state of Singapore. It’s actually kind of a funny story. When we were doing our pilot testing back in the mid nineties, Singapore visited us to see what we were doing. And we actually shared a lot of data that we had out of that, which helped them lead to the development of potable reuse in Singapore.

They probably by far have done the most overall, as far as potable reuse. They probably right now have a combined capacity, several different plants throughout the country, in excess of 150 million gallons per day.

And also a couple of very large projects on the book. Metropolitan Water District of Southern California, in conjunction with the LA county sanitation district is planning a 150 million gallon per day potable reuse project. And the City of LA, uh, along with city sanitation is looking at an equally large facility also down at their Hyperion plant, a very large regional plant down near the LA airport.

So those two projects, it’ll take them time. They’re in the early stages. Uh, but what’s interesting is both those projects may utilize the water in a more direct use, what we call direct potable reuse.

Jay: So it’s really great to hear that, um, your pioneering efforts are really catching on around the world. Really. And now, before I go, I want to ask you about, we talked a little bit about desalination. So, I mean, what do you think in terms of the pros and cons of desalination?

Mike: I think at some point in time we will have to look to the ocean for another source of water. I mean, we talk about a portfolio approach, Jay. We’ve got to look at stormwater capture. We’ve got to look at recycled water. We mentioned, uh, water use efficiency or conservation.

Uh, at some point in time, you know, it’s so unpredictable with climate change. If all of a sudden California gets shut off from its imported water supplies and has to solely rely on local supply, there just isn’t enough wastewater that we can recycle to take care of the water demands in the area.

And if that were the case – and that’s a real extreme case, in my opinion – it’s only then that we would probably be developing seawater desalination. Although there is a plant, as you may know, down in Carlsbad between LA and San Diego. It’s about a 50 million gallon plant that’s in operation, that has been in operation.

So, I mean, the process works. It can be built in an environmentally safe manner. So it is there it’s just a matter of costs and I think somewhere in the future, it will become a more real than it is today. 

Jay: You have spent so much time on this and it’s working out so well. You must have some personal gratification, you must feel right. How do you feel about what you’ve been able to pioneer? 

Mike: You know, I feel so blessed. I mean, to be given this opportunity, it just kind of fell on my lap and I’m so thankful and, to see it work, it is so gratifying. Obviously, I wouldn’t have gotten here unless I had some really good people around me also. And it was a team effort and everyone in the team was committed to making sure that it was going to work and that it has worked. And I do reflect on that and consider myself very fortunate to have been put in that position. 

Jay: Well, I mean you’ve done an amazing, amazing job. And I think 20, 30 years from now, you’re gonna look back and see this stuff all over the world. We talk a lot about climate adaptation and adapting water management, and you’re literally working on something that is having a huge impact.

So, you know, kudos to you, Mike, and to the team at OCWD and the Groundwater Replenishment System, just really fascinating work and incredible contribution. 

Mike: I really appreciate that, Jay. Thanks. Thanks so much. 

Jay: Mike Markus is the General Manager of the Orange County Water District in Fountain Valley, California. Tthe American Society of Civil Engineers named Mike a pioneer in groundwater in 2017.


Jay: As we heard from Mike, one day, we may need to turn to the ocean for water we can drink: turning saltwater into fresh. A team of researchers at Stanford is trying to make desalination more viable, more safe for the environment and less costly. Dr. William is an assistant professor of chemical engineering at Stanford university.

William Tarpeh: Desalination has a ton of great opportunities. Of course, we need to make non-potable water into potable water. And so we need to use lots of non-traditional source waters as we often call them. I think some of the major challenges with desalination are, um, energy, of course, energy consumption and how to do this energy efficiently.

And another that’s sort of increasingly recognized as what to do with the saltier water that you make, the brine or the concentrate. And especially if you’re doing inland desalination, the question is: where do you put the saltier waste product?

So we’re a lab focused almost completely on wastewaters and what to do with them and how to make them more valuable and kind of do two things at once, uh, remove pollutants and create something valuable from them.

And so this has been our entree into desalination is what to do with this very salty, very concentrated brine, especially when it’s coming from processes like reverse osmosis. Uh, so we’ve been thinking a lot about what are some costs and energy efficient ways to recover valuable products from reverse osmosis concentrate, and we’ve been using electricity to do so because it can be cheap (especially if we’re using renewable electrons), scalable, and also allows us a lot of modularity.

That’s our dream, is to be able to have this product or multiple products, actually that come from this reverse osmosis concentrate waste stream. And so the products we’re most considering right now are things like sodium hydroxide. So sodium chloride is the big salt that’s in this brine. So we can make sodium hydroxide and then hydrochloric acid.

You might think about selling them and putting them into the commodity chemical market. What’s really fun is there are also uses right at the desalination treatment plant for these acids and bases. So you might be able to just kind of use them onsite and then offset some of the purchases that the desalination plant is making.

I think we definitely need to keep doing more desalination, especially in arid regions and places stricken by drought. And I think we have the advantage of being able to start thinking about the waste products right now, rather than waiting 10 years. And then trying to say like, “Oh my gosh, now we have this huge volume of waste brine. What are we going to do with it?” And to be fair, lots of installations pump that brine into the ocean and the jury is still out. There are conflicting reports on the effects of that in terms of aquatic ecosystems. But if there’s one thing we know is that when you scale up discharge, it gets more complicated.

It might be fine at the level we’re doing it now. But if the number of desalination plants increases a hundred fold, we probably need to start thinking about better waste management, concentrate management strategies. So there are lots of opportunities. So this is definitely a field where we could use more help and more brilliant minds.

Jay: Dr. William Tarpeh is an assistant professor of chemical engineering at Stanford University.

That’s it for this episode of what about water? We record and produce this podcast on Treaty Six Territory, the homeland of first nations and Métis people. It’s produced by the Walrus Lab and the Global Institute for Water Security at the University of Saskatchewan. For more resources, check out

Our crew here at What About Water? is Mark Ferguson, Erin Stephens, Laura McFarlan, Fred Reibin, Jesse Witow, Shawn Ahmed, and Andrea Rowe. Our audio engineer is Wayne Giesbrecht and our producers are Farha Ahktar and Jen Quesnel. What about Water is available on Spotify, Apple, and wherever you download your favorite podcasts.

I’m Jay Famigiletti. Thanks for listening.