The Southwest Offers Blueprints for the Future of Wastewater Reuse
By turning wastewater into drinking water, our existing water supplies could go further.
No country is immune from water scarcity issues—not even the world’s wealthiest country, the United States.
The Southwestern states, in particular, have faced frequent and ongoing droughts over the past two decades, and traditional water supplies are failing. As groundwater supplies in the region have depleted substantially, rainfall has decreased and the costs of importing water have risen substantially.
The region looks to the Colorado River as its plumbing system, which currently provides drinking water to 1 in 10 Americans—all while irrigating nearly 5.5 million acres of land. But it’s also being stretched to its limits: Population growth and expansive development are increasing agricultural demands. Meanwhile, the pressure to ensure that there is sufficient water left in the environment to support ecosystems has accelerated. According to a study by the U.S. Department of the Interior Bureau of Reclamation, the demands on the Colorado River are expected to exceed supply by 2040.
On top of this, each state has vastly different needs. For example, Nevada’s needs are largely urban, but Arizona and California require water for huge agricultural and urban sectors. Each year, states argue over who has the superior right to water supplies. And once they have their allocation, districts frequently end up in litigation over their allotment. There is always a shortage, raising questions over who is responsible and who must mitigate for it.
Of course, these variables can change year after year, and all planning is dictated by a largely unpredictable snowpack and, therefore, an increasingly erratic river flow. While demand is increasing, climate change has damaged supply—and the impact is twofold, as less water comes down the Colorado River and people use more water due to increased temperatures.
Simply put, there is only so much water.
“When you can’t make the pie bigger and you’re fighting over a finite supply, it’s a misery index, just an allocation pain for all parties,” says Brad Herrema, a lawyer who specializes in water law and natural resources.
“But if you can make the pie bigger, there’s less fighting.”
Turning Wastewater Into a Resource
Our existing water supplies must go further, and the technology exists to make this happen—by turning wastewater into drinking water. This is not a new science, but the practice has evolved significantly in the past 50 years.
In the 1960s, water availability became problematic in rapidly growing areas in the U.S., and water managers began to consider using wastewater to augment supplies. A number of water reuse projects were built in the following decades in California, Virginia, Texas and Georgia, but larger developments in the 1990s were met with opposition. “Toilet to tap” narratives in the media fed misperceptions regarding the treatment process, which helped to dismantle public support for these projects. What “toilet to tap” now misses is membrane filtration, membrane desalination, ozone and advanced oxidation, to name but a few treatment options that make the purified water entirely safe to drink.
But advances in these very technologies associated with water reuse helped boost confidence in and acceptance of the practice among water professionals in the early 2000s. Now, water reuse is entering the mainstream.
Almost half of all the potable reuse projects built in California, since the first in 1962, have been installed in the past 10 years, with several more on the horizon for the early 2020s. California—with more potable reuse projects than any other state—used around 1.5 million acre-feet per year (AFY) of reused water in 2020, with one acre-foot equivalent to about 326,000 gallons and enough to cover a football field. The state plans to increase this to 2.5 million AFY by 2030, almost doubling the number, especially once planned potable reuse projects are installed.
And according to a document by the Environmental Protection Agency and CDM Smith Inc., potable reuse also makes up “a significant portion” of the nation’s water supply once de facto reuse is factored in.
What’s clear is that some major U.S. cities are already delivering recycled wastewater to the consumer on a massive scale and making the pie larger.
How a city can recycle wastewater depends largely on the geography of the area, financial resources—and, perhaps most importantly, the attitudes of the public.
Las Vegas recycles nearly all of its water used indoors, giving it a virtually inexhaustible supply of water for domestic consumption. The city benefits from its unique geography. Nearly 90 percent of southern Nevada’s water is taken from Lake Mead, which lies on the Colorado River. It is then treated and run through the city’s system. After it’s flushed or drained, the water makes its way to a wastewater treatment plant before it’s discharged into the Las Vegas Wash. From there it makes its way to Lake Mead where it is either drawn back out or stays in the river, ensuring there’s enough water for cities downstream of Vegas.
One key element that makes Vegas’s reuse system so effective is the Wash: a 12-mile-long channel that acts “as the ‘kidneys’ of the environment, cleaning the water that runs through… [it by] filtering out [any] harmful residues” on its way back to Lake Mead. Thanks to the Wash, when the water is withdrawn again, it does not need to go through a costly process of advanced treatment and, instead, undergoes just basic drinking water treatment.
Another key factor in Vegas’s success is that for every gallon of water Las Vegas puts into Lake Mead, it can take a gallon back out—meaning the city is essentially recycling its indoor water in a closed loop. This is known as de facto water reuse.
Nevada is allocated 300,000 AFY of water from the Colorado River each year. Bronson Mack, who oversees water resources and operations at Southern Nevada Water Authority (SNWA), says that in 2019, the city actually diverted 490,000 AFY of water from the Colorado River but only consumed 234,000 AFY. About 256,000 AFY was returned to the lake.
“Our return flow credits system is unique,” says Colby Pellegrino, director of the water resources department for SNWA. “Once we return the water to Lake Mead, we’re not charged for that water. We’re only charged for the total we depleted.”
Mack adds that local water utilities pay $313 for treatment and delivery of 1 acre-foot of water, and pass that cost on to the consumer. If Vegas could not return such a large proportion of its water, that cost would rise dramatically.
De facto reuse is also vital for a city that can’t afford to gamble on the weather—Las Vegas is the driest city in the U.S. When the Colorado River ran at 40 percent of its usual capacity in 2002, the city was struck by drought, but its citizens still had unlimited access to indoor water.
“Vegas couldn’t exist without [the] return flow credits approach,” says Daniel Gerrity, an assistant professor of environmental engineering at the University of Nevada, Las Vegas. “Without that, we’d have already maxed out.”
This means the city’s major conservation efforts go into limiting outdoor use. And so, contrary to expectations, it is not the casinos that are the problem—but the local residents, who irrigate their gardens and wash their cars. After all, water lost to evaporation is water lost forever.
However, not every city has a Lake Mead or a Wash. For places without Vegas’s luck, there are other ways to do water reuse.
Orange County, California
Orange County Water District (OCWD) is a world leader in water reuse. Since 2008, it has provided drinking water to 2.5 million people—in a region with no more than 15 inches of annual rainfall—through its Groundwater Replenishment System (GWRS) project. This water would otherwise be discharged into the Pacific Ocean. By keeping it in the system, there is less reliance on the Colorado River, easing the strain on its supplies.
The city utilizes a process called indirect potable reuse (IPR). In the absence of an environmental filtration process like the Las Vegas Wash, Orange County’s wastewater has to undergo advanced treatment before it is pumped to a groundwater basin. From there, it is pumped to the consumer via a standard drinking water treatment train making it safe to consume and completing the cycle. The process not only turns wastewater back into a resource, but also saves massively on the cost of pumping Colorado River water from hundreds of miles away.
GWRS, which is a joint project of OCWD and the Orange County Sanitation District (OCSD), currently supplies north and central Orange County with 77 percent of its water supply, and it is expanding its wastewater treatment capacity from 100 to 130 million gallons per day by 2023. OCWD’s executive director of engineering and water resources, John Kennedy, says the expansion will save providers in Orange County over $6 million per year as there will be more water available to pump from the basin. Currently, he says, the other 23 percent of the water requirement of Orange County must be bought at approximately three times the price of reused water from another regional wholesaler—the Metropolitan Water District of Southern California—that operates the Colorado River Aqueduct, which is a 242-mile water conveyance. And so, not only does expanding the water reuse projects make the pie bigger, but there’s also an economic incentive attached to it.
“Orange County is the benchmark [for] water reuse system,” says Gerrity.
Water managers from around the world visit OCWD to learn how they’ve managed such success.
Like so many regions innovating in water reuse, drought forced their hand. In 1975, “[a]s imported water supplies became less available, another source of water was needed to fight seawater intrusion. In April 1975, OCWD unveiled… [a facility that] took treated wastewater from the… OCSD, blended it with deep well water and injected it into… [a basin]. In 1977, [OCWD became]… the first in the world to use reverse osmosis to purify wastewater to drinking water standards.”
The project was expanded in line with the demand in the ’90s, and the GWRS, which has been operational since 2008, is now the world’s largest advanced water purification system for potable use.
And through it all, OCWD managed to swerve the “toilet to tap” attacks that had ruined public support for such projects in other areas of California.
“People expect to find out that our success is grounded in some secret technology, but they find out it’s all about education, education, education,” says Rob Thompson, the director of engineering at OCSD, which treats the water before sending it to the basin managed by OCWD. “Bringing the public on board with drinking [recycled] wastewater takes a lot of outreach. Getting over the ‘yuck factor’ is everything. We had to speak with NGOs, governors, the authorities, politicians—you name it, we spoke to them. Once you have enough people on board, everyone starts to think it must be okay.”
“People have high expectations about the quality of their water and have a lot of questions,” adds Dr. Megan Plumlee, who heads OCWD’s research and development department. “We explain to the public what we’re doing and how it’ll benefit the district, retailers and community.”
San Diego, currently embarking on a huge potable reuse project, followed OCWD’s lead when developing their project. Indeed, sometimes it takes a leader in the field for a new process to take hold, someone to show the way and prove something can be done safely, on a large scale.
“We weren’t the first to try it, but we were the first to succeed on such a massive scale. That’s because we were the first to really embrace education. Now others are doing the same,” says Thompson.
Now, 14 states have developed regulations that allow for IPR, with several more IPR projects on the horizon that will help bolster water supplies—all without putting additional pressure on the Colorado River.
Another method of water reuse, which is more efficient, is yet to take hold in the U.S.—though it may be about to find its leader.
Direct potable reuse (DPR) was labeled the final frontier of water reuse by G. Tracy Mehan, the executive director for government affairs at the American Water Works Association (AWWA), in an essay written for A Better Planet: 40 Big Ideas for a Sustainable Future. The process does away with an environmental buffer and pumps wastewater directly through an advanced treatment train before it is purified and put straight back into the system in a matter of hours.
Given this reality, DPR can deliver water more efficiently and cost-effectively by using existing infrastructure and without needing to build expensive and energy-intensive pipelines to a reservoir or groundwater basin. DPR can also allow for more water to be recycled than IPR as there are no limitations on the reservoir or groundwater basin.
Additionally, DPR avoids regulations on putting water back into the environment by eliminating the buffer. And finally, DPR can be more reliable and efficient: Jeff Mosher, vice president and principal technologist at Carollo Engineers, a leading firm in engineering water reuse systems, explains that DPR can turn wastewater into drinking water in a matter of hours, faster than IPR or any other method of reuse.
Only two facilities in the U.S. are currently equipped to operate DPR—both are in Texas. Big Spring in West Texas identified DPR as the most feasible way to address an urgent need to diversify the city’s water portfolio and increase its supply reliability for when rains failed to fill the city’s reservoirs—the project now serves around 135,000 people. Wichita Falls in northern Texas, serving 150,000 people, followed Big Spring’s example. Anticipating a water crisis with the city reservoirs at less than 20 percent capacity in 2012, and lacking a groundwater backup supply, Wichita Falls determined DPR was a viable means of urgently meeting potable water demands. The two systems can supply 2 million and 5 million gallons per day, respectively.
Both facilities have been successful and without incident, yet the catalyst for both was an emergency. Such was the water crisis both cities were facing, that Texas had to use emergency water regulations in order to build the facilities without formal DPR regulations. DPR is yet to become a mainstream and a trusted water supply system, and it still remains unused outside times of crisis and for larger communities.
Only Arizona has draft regulations that allow for DPR (while formal regulations are drawn); California, Colorado and Florida are actively pursuing regulations. This is mainly due to a lack of public acceptance. The speed at which DPR recycles wastewater makes it particularly vulnerable to “toilet to tap” attacks, and this has consumers concerned, who worry over the small room for error and the “yuck factor.”
An attempt to introduce potable reuse in San Diego in the 1990s failed after fears of “drinking sewage” diminished trust in the project and fostered uncertainty about the safety of the water.
And in 2005, just 28 percent of people randomly surveyed in San Diego strongly favored or somewhat favored using advanced treated recycled water to supplement the drinking water supply.
San Diego has changed its mind and now it may one day do for DPR what OCWD has done for IPR and pave the way for DPR use on a wider scale.
With lessons learned from OCWD, outreach helped bring the community on board in San Diego. “We had to educate the community on the concept [of potable reuse],” Amy Dorman, a senior engineer on San Diego’s Pure Water program, says. “We ran focus groups with the community, made ourselves flexible moving forward and recognized the importance of listening to the community. In the ’90s, there was not the right amount of education. Now it’s comprehensive. We do tours, presentations, websites, mailers and [identify] all stakeholders—[ensuring] diligent and constant outreach.”
Dorman explains that 18,665 San Diegans have visited the demonstration facility, while the team at Pure Water has spoken to almost 30,000 children in schools. They explain that 50,000 lab tests have been carried out on the water supply, each meeting every regulatory standard and producing exceptional water quality—typical tap water is actually less highly treated than DPR tap water.
But the key statistic is that 85 percent of San Diego’s water is already imported from the Colorado River and Northern California Bay Delta. In fact, because the city is downstream, Dorman says that the water has already been recycled 49 times by other water districts before it reaches San Diego. She says this usually quells fears that drinking recycled water is unsanitary, since, as it turns out, residents have been doing it for years.
“What we know now is that it’s possible to convince people,” adds Mosher. “We have proven that every community you go into that has concerns, you can overcome.”
San Diego hopes that by 2035, a third of the city’s supply will come from locally supplied, recycled wastewater instead of importing the majority of its water supply.
For phase one, the Pure Water San Diego program—funded by the San Diego government—will use IPR to provide the city with 30 million gallons of water per day, utilizing the nearby Miramar Reservoir as an environmental buffer in a similar way to how Orange County uses its groundwater basin.
But phases two and three target an additional 53 million gallons of water per day. In the absence of a groundwater basin and large enough reservoirs, Pure Water San Diego plans to employ DPR to realize the project’s full scale.
Mosher says that cities with plans to do DPR one day don’t want the attention, to be the ones to take the dive into doing it on a large scale. But with projects on the horizon in San Diego, as well as El Paso, Texas, Mosher expects greater faith in the process by the end of the decade, and a 2011 public opinion poll shows that citizens are 50 percent more likely to accept recycled water when they learn that other communities have done so already.
Without a leader in the field, there is hesitancy among cities interested in doing DPR, but Gerrity is positive about the impact San Diego can have countrywide.
“It’s a good platform to go forward,” he says. “We have more options for facing water scarcity, another tool in the toolbox to tap into. Conservation, potable reuse [and] innovative technologies all extend supply and give high-quality drinking water to the public.”
Mainstreaming Potable Reuse
While water reuse is breaking into the mainstream, there are still challenges going forward.
It is not simply a matter of copying Las Vegas, Orange County or San Diego. The geography and finances of a region often dictate a city’s water supply—and that has a huge impact on what kind of reuse that city can attempt. De facto reuse, as in Las Vegas, is incredibly site-specific and requires the geography of an area to substitute for advanced treatment, while the most successful IPR projects rely on large groundwater basins and nearby reservoirs.
Both types of potable reuse are also incredibly expensive, and while they may save money in the long term, they require a huge initial investment. The advanced water purification facility in Wichita Falls, for example, cost $13 million. OCWD, serving 2.5 million people, will have spent upward of half a billion dollars once the final phase of their project is complete, almost doubling their initial outlay. Irrespective of the size of your service area, installing an advanced treatment facility is expensive.
There are ways to get around the financial obstacles, though.Districts not doing potable reuse may help fund water reuse projects in exchange for a greater share of the pie. Take Las Vegas, for example. It makes no sense for SNWA to build an advanced water purification facility—the city’s proximity to Lake Mead keeps pumping costs low, and the lake itself acts as a natural cleanser. However, SNWA is currently in discussions to potentially fund potable reuse projects in California in exchange for additional water from the Colorado River.
Gerrity says this could happen on a wider scale. “Anywhere with water scarcity, it’ll make sense for us to realize, by investing in water infrastructure, we can alleviate problems.”
And working out what works best for one community is half the battle. Because there is no one size fits all thanks to the geographical nuances that help potable reuse or de facto reuse work.
“You could take what Orange County does, and it’s going to work, but the question is whether that is the best approach for that location. So, the challenge is, now that we feel comfortable with one approach, can we do it a different way?” says Gerrity.
Mosher is trying to compile all the information on water reuse into an easy-to-read guidance document that cities considering the process can use to decide which approach may be best for them.
“It’s about getting to a point where communities who want to try DPR don’t feel overwhelmed,” says Mosher.
What’s clear is that the Colorado River can no longer be relied upon to provide such vast numbers of people with their water needs. If we are to continue asking so much of it, then we have to start easing those pressures. Water reuse is a future imperative if the driest parts of the world are to continue growing without destroying the environment that relies as much on water as we do.