Scientists haven’t found any evidence that suggests the city of Flagstaff’s use of reclaimed wastewater puts human health at undue risk.

That was the conclusion reaffirmed earlier this month by a panel of experts tasked with evaluating the city’s use of treated effluent at places like golf courses, city parks and the slopes of Arizona Snowbowl.

The city can produce up to 10 million gallons a day of A+ wastewater that officials contend is 99.9 percent pure, although it is not rated safe to drink. It's that last 0.1 percent that officials not just in Flagstaff but across the country are interested in learning more about.

The group of water and genetics experts, university researchers and medical professionals was first organized five years ago at the request of a former city manager in the face of mounting local concern over the potential human health effects of reclaimed wastewater use.

The group reconvened Nov. 3 to review a final report on the city’s reclaimed wastewater testing as well as results of panel members’ own research on antibiotic-resistant genes and bacteria in Flagstaff’s water system. In short, the city’s own testing and the scientists’ research found evidence of certain unregulated substances, collectively classified as compounds of emerging concern, in Flagstaff’s drinking water and reclaimed wastewater.

But based on concentrations and types of substances detected, the panel didn’t see cause for concern about those findings.

At the end of their meeting, the members reaffirmed their conclusion that no data at the present time suggests that reclaimed wastewater use in Flagstaff is dangerous to human health.

“I don’t see any reason to stop using reclaimed wastewater, there was nothing alarming about it,” said Amy Pruden, an environmental engineering professor at Virginia Tech University and one of the panel members.

The work showed that the city is “comparable or better” than other places in its use of reclaimed wastewater, Pruden said.

Other tests of the bacteria present in Flagstaff’s reclaimed wastewater didn’t raise any red flags either, said Jean McLain, the associate director of the University of Arizona’s Water Resources Research Center and another panel member.

“The recycled water in Flagstaff, from the standpoint of living bacteria, was as clean or more clean than the other municipal systems tested,” McLain wrote in a follow up email.


When it first met in 2013, the panel decided to focus on compounds of emerging concern, or CECs. The group of substances includes pharmaceuticals, personal care products and endocrine disruptors. They are not regulated by the federal government, though they may have the potential to cause adverse health or ecological impacts.

Upon the recommendation of the panel, Flagstaff’s Water Services department committed to testing its potable and reclaimed wastewater for CECs. Between 2010 and 2015, city staff sampled a total of 20 locations in its reclaimed and potable water systems. Each water source was sampled one to three times and was analyzed for up to 95 CECs, including four substances that were specifically recommended by the advisory panel.

The results showed the presence of CECs in both potable water and reclaimed wastewater flowing through the city’s system. The amounts detected, however, were described by the city as “trace concentrations” similar to those found in sampling efforts dating back to 2002.

The number of compounds detected and their concentrations were, in general, much higher in the reclaimed wastewater, with 64 different CECs detected in the reclaimed wastewater samples versus 22 CECs detected in the potable water samples.

In its review of the results, the advisory panel did not recommend that the city to conduct further sampling, and the city indicated it wouldn’t continue sampling for CECs unless that recommendation changes in the future.


In addition to its own water testing, the city contributed samples of its water to three research projects that zeroed in on antibiotic-resistant genes. The genes are classified as CECs and present a threat to human health because they can confer pathogens with the ability to resist antibiotics, making them extremely difficult for doctors to treat.

The research projects analyzed water samples from Flagstaff and three other utilities for the presence of antibiotic-resistant genes and then assessed whether those genes were associated with bacteria that actually had the potential to grow and survive treatment by antibiotics.

A Virginia Tech research team did find antibiotic-resistant genetic material in both potable and reclaimed wastewater in Flagstaff. Their tests found both types of water contained genes that confer resistance to four antibiotics classified as highly and critically important, though the gene counts were either equivalent or higher in reclaimed wastewater, said Pruden, who led the study.

Flagstaff’s TGen North also analyzed the city’s water, but found no indication of bacterial species of concern nor antibiotic-resistant genes in drinking water, which is a different finding than Pruden’s study. The TGen testing did detect the resistance genes in certain bacteria that were living in Flagstaff’s wastewater.

The takehome message from both research groups, however, is that the presence of antibiotic-resistant genes doesn't mean Flagstaff’s drinking water or reclaimed wastewater is crawling with dangerous antibiotic-resistant bacteria. The material detected could be inside dead bacteria or bacteria that aren’t pathogenic or could be free-floating DNA not associated with any organism, said Jolene Bowers, a research assistant professor at TGen, which is a nonprofit genomic research institute.

Resistance to antibacterials also isn’t necessarily a product of superbugs developing in hospitals and then spreading throughout the water system. Bacteria also acquire resistance via the environment as they interact with and fight off chemicals produced by other bacteria, said Dave Engelthaler, director of TGen North.


A different research team from the University of Arizona sought to answer the question left hanging by the other DNA analysis tests--are the antibiotic-resistant genes associated with any bacteria that have the potential to grow, multiply and survive through a dose of antibiotics?

Those are the ones that present the true risk, said McLain, who led that project.

The researchers focused on two bacteria, E. coli and Enterococcus, which are of interest to scientists because they can cause serious infections and have multiple drug-resistant strains.

The study had two positive findings for Flagstaff’s water and the effectiveness of its treatment processes: there was no evidence of either type of bacteria in the city’s drinking water samples and no viable E. coli bacteria in Flagstaff’s reclaimed wastewater.

Researchers did find five Enterococcus bacteria in the reclaimed wastewater, each of which was resistant to at least one of the antibiotics tested.

But McLain echoed Engelthaler in pointing out that Enterococci are found naturally in soil and water, and antibiotic resistance is also a natural phenomenon.

“There was nothing found in our research that suggested that recycled water is spreading living bacteria in Flagstaff,” she wrote in a follow up email.


While the panelists cleared Flagstaff for continued use of reclaimed wastewater, several said lots of work remains to be done to understand the impacts of CECs on human health. Scientists are still trying to figure out which antibiotic-resistant genes may pose a risk to human health, in what concentrations and via which pathways, Pruden said.

“Right now we have no idea,” she said.

The same thing goes for CECs in general, said Robin Silver, who is a practicing physician and a member on the panel. There isn’t any hard science that says exposure to a certain amount of a specific compound is unsafe, said Silver, who is also the cofounder of the Center for Biological Diversity.

While CEC concentrations in Flagstaff’s water are pretty low in terms of what has been established for human disease, the physicians in the group feel that it doesn’t take much of something like an endocrine disrupter to cause an effect, Silver said.


Several panelists lauded the city of Flagstaff for creating the water advisory panel, conducting its own extensive water testing beyond what current regulations require and supporting research about bacteria and genes in its water.

“Flagstaff has really been thrown into the spotlight as a real leader in doing this research,” Pruden said. “I’m not aware of any other city that has publicly done this kind of research at this scale and we learned a lot.”

Emery Cowan can be reached at (928) 556-2250 or