Data centers sprouting up across the U.S. are facing an emerging environmental challenge: What happens to the wastewater they generate, and what kind of contaminants are in it?
Recently, a data center under construction in Cheyenne, Wyoming, was found to have contaminated the sewer system with a rare bacterium.
The water utility took swift action. The Cheyenne Board of Public Utilities fined the project developer, revoked its wastewater permit and announced that it would not accept certain types of wastewater from data centers citywide.
The developer of the project — which is backed by Meta — is appealing the $10,000 fine and disputes the utility’s conclusion tracing the bacterium to its project.
But the incident highlights what engineers view as an emerging challenge for the data center industry that is already under scrutiny over its environmental footprint. As new projects crop up nationwide, experts say it’s not clear whether small utilities have the infrastructure and regulations to ensure the wastewater is properly managed.
“It’s almost like overnight, we have a new industry. Normally when it comes to industrial discharges, the information is public and also well documented,” said Jonathan Brant, an engineering professor at the University of Wyoming.
With data centers, there is “scant actual hard data out there on what these waters look like or how these waters are going to be managed,” Brant said.
Powering AI’s rise are an influx of large, powerful data centers that each contain up to hundreds of thousands of computer chips. Some use water to keep those chips cool, while others primarily rely on electric power — a trade-off that can result in projects consuming huge amounts of electricity or guzzling millions of gallons of water per day.
But it’s in the long process of building a new data center where wastewater concerns first arise. The initial build can produce wastewater that local sewer systems may not be used to — and which current regulations might not address.
“The regulatory processes for industries that EPA has are really meant for once it’s constructed and operated. Then you issue them a permit and they have to report to you,” said Kendra Sveum, operations director at Loudoun Water, the utility serving northern Virginia’s data center hub. “There’s really not a system in place for these construction activities.”
To help prevent computer chips from overheating and malfunctioning, most data centers being built now use a closed-loop system that continuously circulates liquid through a sealed pipe.
“Closed-loop” is sometimes used as short-hand for water-efficient data centers. But it has little to do with a data center’s actual water usage, as that depends on whether the data center uses water to expel heat from the building, said Shaolei Ren, an engineering professor at the University of California, Riverside.
Instead, the circulation of liquid coolant through contained pipes is a virtual necessity in modern data center design, providing extra protection against overheating of chips, Ren said. The water can circulate for months or years before it needs to be disposed of and replaced.
“Almost every AI data center today, you’re going to see some type of these closed-loop systems,” Ren said. “So as more data centers are using this type of cooling system, the wastewater discharge is becoming an infrastructure consideration.”
Cheyenne may have learned that the hard way.
Prior to beginning operations, a data center must clean its closed-loop pipes. The process is known as “fill and flush,” wherein water gets circulated through the pipes — sometimes with the addition of chemicals to prevent pipe corrosion — to remove bacteria and other impurities.
What’s left behind is wastewater with contents that utilities may not recognize.
It’s that type of wastewater — fill-and-flush discharges and other wastewater from closed-loop cooling systems — that Cheyenne’s utility says it will no longer accept.
“We’ve set up a rule that says, ‘You will not discharge to the public wastewater system, period, until we learn more about what’s going on and can understand exactly what happened,’” Bryce Dorr, an engineer with Board of Public Utilities, told the Cheyenne City Council last week.
The decision came after utility staff discovered a strange bacterium, cupriavidus gilardii, in the sewer system in February. The finding was alarming because the bacterium remained in wastewater after it was treated and reused to irrigate a golf course as part of a water conservation program. Following an extensive investigation, the utility traced the bacteria to the data center in the southern portion of the city.
Meta’s contractor, Fortis Construction, argued that the sewer board hasn’t provided evidence to prove that the contaminant came from its project. It filed an appeal last week to dismiss the fine and get its permit reinstated.
“When the issue was first raised, our contractor immediately stopped releasing water into the wastewater system and hauled it off-site,” Francis Brennan, a Meta spokesperson, said in a statement. “Subsequent independent, third-party testing — including at least one test conducted in conjunction with the Board of Public Utilities — detected no bacteria. However, the Board has not shared all of its underlying testing data or other information with Meta, our contractor, or the public.”
Fortis Construction did not respond to multiple requests for comment.
‘We pay very close attention’
If there’s anyone in the sewage treatment business who understands how to deal with data centers, it’s Sveum. At Loudoun Water, she helps manage wastewater from more than 200 data centers in northern Virginia’s data center alley.
Not all water that the facilities send to the sewer system is problematic, Sveum said.
Data centers that use water evaporation to reject heat routinely discharge what’s known as blowdown water. The evaporative process can concentrate whatever contaminants that were in the water to begin with, such as solids and salts, but it’s still similar to what’s generated from commercial buildings and homes, Sveum said.
Similar to the Wyoming project, problems have popped up during the construction of closed-loop pipes, she said.
And in Loudoun County, data center construction has been near-constant for over a decade.
“The construction of those loops, we pay very close attention to, because that process … can use chemicals that aren’t really suitable for wastewater treatment,” Sveum said. “We put [a] process in place essentially as we experienced issues over time. We realized we needed a control mechanism.”
Data center developers must now test the flush-and-fill water produced during construction before it can be sent to the treatment plant. Loudoun Water also verifies the results independently, Sveum said.
In some cases, the utility has taken issue with the wastewater and directed data center developers to send it to “an appropriate facility” for disposal, she said.
“A lot of smaller utilities are being faced with these challenges. We like to share that Loudoun Water makes [data centers] do this, so they can too,” Sveum said.
Across the U.S., most data centers send wastewater to local treatment plants instead of discharging directly into nearby waters, said Wangusi Barasa, the former director of water sustainability at Amazon who now runs BlueCredit, a water consulting firm.
In general, the biggest risks for utilities receiving the water is if it contains contaminants that the treatment plant cannot remove or that interferes with treatment itself.
If chemicals, metals or nutrients like phosphorous remain in the wastewater after treatment, they can recirculate in rivers, lakes or streams — and utilities may face fines if the levels exceed what’s allowed under their permit.
“You’re concentrating whatever was in the source water. That’s a problem if you’re doing it continuously and in large volumes,” Barasa said.
Last December, Ohio proposed a general permit that would make it easier for data centers to be approved to send wastewater directly into nearby waters instead of to a municipal treatment plant.
The proposal drew criticism from environmental groups and members of Ohio’s congressional delegation, and more than 7,000 people filed comments to the state. Ohio EPA has not taken further action.
‘Should never have happened’
It’s not clear how a rare bacterium may have gotten into the wastewater from the Cheyenne data center.
While Loudoun Water has faced issues with data center discharges containing high levels of metals and nutrients, there’s never been an issue with bacteria, Sveum said.
Brant, the University of Wyoming professor, said the bacterium identified is known for proliferating when copper is present. But he has questions about why it would have had time to proliferate in the closed-loop pipes, given that the fill-and-flush process should not have taken very long, and why the utility was even testing for the substance.
Either way, he’d like to see stronger regulations on data center wastewater.
“Do I think there need to be changes? Absolutely,” he said. “And a lot of it is improving the transparency. Stop using little anecdotes, like, ‘[We’re] only using six bathtubs or 10 bathtubs of water.’”
Brennan, the Meta spokesperson, said fill-and-flush is a critical step for commissioning a data center’s pipes before it’s turned on. Although Sveum said some data centers flush out those pipes several times, Brennan said it was a “one-time step” for the data center in Cheyenne.
Meta further described the fluid from fill-and-flush as a “known, monitored” substance that does not contain industrial contaminants. The company also said that it tracks what’s in the water produced by its data centers.
It’s not clear how many data centers in Cheyenne could be affected by the utility’s ban on wastewater from closed-loop pipes. The Cheyenne Board of Public Utilities declined to make someone available for an interview and did not answer written questions.
At the city council meeting last week, Dorr — the utility engineer — said there’s no evidence that the bacterium was intentionally added to the data center pipes. But after the substance was identified, the utility shut down its water reuse system for several months due to the risk of human infections from exposure.
It took extensive efforts to remove all traces of the substance from Cheyenne’s sewer system and water reuse operations, according to the utility. The $10,000 fine was meant to help cover those costs.
The utility is “still trying to understand what happened,” Dorr said. In the meantime, some local officials in Cheyenne said the incident should be a sign that data centers need more oversight as the industry grows.
“This was a problem that should never have happened, and I’m still not certain how it did,” said Peter Laybourn, a member of the nonpartisan Cheyenne City Council. “We’re welcoming to data centers and have done well on it so far, but you need regulation.”
