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For a landlocked state, Colorado is wild about water. We swim in it, paddle in it, and (when it’s cold enough) ski on it. Plus, our H2O is delicious. Last year, one ranking of the best-tasting water in the United States and Canada gave Grand Junction the silver medal, while another list hailed Eldorado Springs as having the fifth-best municipal water worldwide. “We’re really fortunate to have pristine water sources coming out of the mountains,” says Nicole Poncelet, Denver Water’s director of water quality and treatment. “We’re largely a first user of raw water coming off the snowpack and the streams.”

But as much as we would like to believe that the precious resource flows straight from the mountains to our mouths, it takes a lot of work to make that water potable. Fifty years ago, Congress took a major step to protect public health by passing the Safe Drinking Water Act, which authorizes the Environmental Protection Agency (EPA) to set standards regarding contaminants, treatment, and how public utilities operate. Before the legislation was enacted, only 60 percent of surveyed systems met federal guidelines. By 2017, more than 90 percent of Americans enjoyed water that matched the standards.

Nevertheless, the world has changed in five decades. Aging infrastructure, warming waters, more intense wildfires, and human-made chemicals all threaten the quality of drinking water. In 2019, water pollution was responsible for 1.4 million premature deaths globally, according to a study published in the Lancet Planetary Health. Tainted water can increase people’s risk for certain cancers, cause gastrointestinal problems, and lead to developmental issues in children.

Twenty states rely on water from Colorado’s major river basins, which means maintaining the health of watersheds here in Colorado is crucial to the well-being of a large swath of the country. Photo by Getty Images

The risks aren’t shared equally, though. Those experiencing poverty, folks living in rural areas such as Colorado’s Arkansas River Valley, and people of color are more likely to lack access to clean water. In April 2022, after 20 years of work, the Southern Ute Indian Tribe in southwest Colorado became only the 47th out of 574 federally recognized tribes to have its water quality standards approved by the EPA under the Clean Water Act.

The good news is that the experts are on it. “Our community—the water nerds of scientists and engineers and chemists and operators and managers—we’re working on and thinking about these things all the time, every day,” says Chad Seidel, president of Corona Environmental Consulting, a national firm that focuses on water issues and has an office in Louisville. What does that look like? We outline some of the biggest threats to the Centennial State’s drinking water—and what’s being done to address the hazards.

3 Ways You Can Help Reduce Water Contamination

1. Don’t flush expired medications down the drain. Instead, find a takeback location through the Colorado Department of Public Health & Environment (CDPHE), which maintains a list of safe disposal sites.

2. Mix your own cleaning supplies using ingredients like vinegar and baking soda instead of relying on chemical blends that will eventually need to be removed at a treatment plant. Bonus: It’s also a money saver.

3. Take your Subaru to the car wash. When you clean the muck off at home, you not only waste treated water, but all that grime runs into the storm drains and can negatively affect watersheds. Car washes generally recycle their dirty water.

How Denver Water Makes Our H2O Safe for Our Bodies

Capable of treating about 600 million gallons a day, the public utility supplies 1.5 million people in the metropolitan area with clean water. Here’s how.

Illustration by Headcase Design


As rain and snowmelt gather and flow through the South Platte, Blue, and Fraser Rivers, the water picks up naturally occurring salts and metals such as aluminum and uranium.

Animals walk, eat, and, yes, poop in the surrounding landscape. Pesticides, chemical contaminants, and bacteria such as E. coli can also wash into streams and reservoirs, as does organic material that sheds from trees and soils.


Step 1: Flocculation. Positively charged coagulants (typically, a metallic salt) are added to the raw water. They connect with the negatively charged particles—like dirt—and form heavy clumps, which drop down to the bottom of the basin. That sludge is pumped to outdoor drying beds; once dried, it’s either blended into a topsoil or shipped off to a landfill.

Step 2: Filtration. The water flows through a six-foot-deep filter made of anthracite coal, which catches minute microbes such as giardia while the cleaner water continues onward.

Step 3: Disinfection. Chlorine is added to kill or deactivate any lingering microorganisms, such as typhoid and cholera, that can sicken humans.


Around 3,000 miles of water mains deliver the now-potable water to customers. To ensure contaminants aren’t leaching into the pipes post-treatment, Denver Water has placed monitors throughout the distribution system to continuously check the product.

1. Lead

Threat Level: High

From our building materials to our automobiles, lead mined from underground helped fuel America’s growth during the first half of the 20th century. Only later did we confront how toxic the substance is: Exposure to the metal can harm brain development and cause anemia and fertility issues. For that reason, the EPA requires corrective action when the amount of lead in public drinking water exceeds 15 parts per billion (ppb)—and in 2012, Denver Water discovered that 10 percent of samples taken for lead testing topped that. The culprit? Customer-owned service lines, from which lead was leaching into the treated water as it moved from the utility’s mains and into homes.

After years of research and wrangling with the state health department, Denver Water launched a Lead Reduction Program in 2020 that simultaneously works to control the water’s pH levels (less acidic water is less likely to corrode metal), replaces old lead lines with copper ones, and provides homeowners with filters to keep them safe in the interim. Denver Water’s Nicole Poncelet says the city has become “a national leader in how to remove lead and reduce lead in people’s tap water.” We break down the program’s impact four years in.

Photo illustration by Headcase Design

Lead Threat to Kids

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Lead is known to be particularly harmful to kids and babies, as exposure to the metal can impede their growth and development, damage their brains, disrupt their hearing and speech, and cause learning and behavior problems. In Colorado, 72 percent of children under six years old have detectable levels of lead in their blood—well above the national average of 51 percent.

So in 2022, Colorado passed legislation that required every public school, childcare center, and family childcare home in the state that serves kids in preschool through fifth grade to test their drinking water for lead by the end of May 2023. For the program, the state also lowered the acceptable lead threshold in those facilities to five parts per billion; if elevated numbers are detected, parents and staff are notified and a remediation plan is required to be submitted to CDPHE within 30 days. As of press time, 1,382 facilities needed to take action. The bill mandates that middle schools participate next; they began testing in September and are required to submit results by November 30.


Threat Level: Medium-High

Last year, environmental groups monitoring Suncor Energy revealed that its Commerce City oil refinery was dumping PFAS—also known as “forever chemicals”—into Sand Creek at rates thousands of times higher than the EPA’s updated drinking water guidelines. With the waterway feeding into the South Platte River, a source of water for thousands of Coloradans, the news alarmed many people, who were left to wonder: What exactly are PFAS and how dangerous are they? We have your answers.

What are PFAS?

PFAS, or per- and polyfluoroalkyl substances, have been around since the 1930s (hello, Teflon). The human-made chemical compounds—there are more than 12,000 types—repel water, grease, and oil. They were also seen as a boon to the manufacturing of carpets, food packaging, water-repellent clothing, nonstick cookware, firefighting foam, and even dental floss. Because PFAS don’t naturally degrade, they have been nicknamed “forever chemicals.”

How do they get into our drinking water?

At least 45 percent of the country’s tap water contains at least one type of PFAS. They wind up there in a variety of ways. When we wash products that contain PFAS, trace amounts are sent down the drain. PFAS-containing items also break down in landfills, and the chemicals can leach into the soil.

How dangerous are these chemicals?

Certain populations, including children five and younger and pregnant and breastfeeding individuals, are more vulnerable to PFAS-related health conditions. Continuing exposure to PFAS can increase the risk of pregnancy-induced hypertension, high cholesterol, and kidney and testicular cancers, as well as decrease fetal and infant growth. West Virginia residents who were exposed to the highest levels of PFOA—a type of PFAS that was once used in the manufacturing of Teflon—from a nearby plastics factory had a 20 to 30 percent higher risk of high blood pressure and preeclampsia during pregnancy. However, there’s still a lot to learn about the substances’ health impacts.

Should we be worried?

In June 2022, the EPA dropped its proposed limit for the two most common PFAS in drinking water to a mark that’s “lower than almost any other chemical scientists have ever studied,” says Sonya Lunder, senior toxics policy advisor for the Sierra Club. At the time, approximately 100 public drinking water systems in Colorado were deemed to have unsafe PFAS levels. As of September, most of the state’s water systems had cleaned up their acts. “We look at this as a concern,” says Ron Falco, CDPHE’s safe drinking water program manager, “but not a crisis.”

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What’s the state doing about PFAS?

As of January 1, new state legislation bans the sale of certain products that contain “intentionally added” PFAS, requires cookware manufacturers to label products with PFAS chemicals, and sets stricter constraints on the use of firefighting foam with PFAS.

How can I ensure my family’s water is safe?

The best way to protect yourself is to determine what testing has been done in your area and read the results. CDPHE maintains a map of PFAS levels in treated drinking water, and utilities inform their customers if they are above the safe thresholds. If you’re in a zone of concern, use at-home filters for drinking and cooking (see below).

The 4 Best Water Filters

Most Coloradans can safely drink their tap water. But if you don’t like the taste, are part of an at-risk group, or want to take extra caution, choose filters that are certified to remove PFAS. CDPHE recommends these.

  1. Cyclopure Purefast filter cartridge, $45
  2. Aquasana clean water machine, $400
  3. Hydroviv under sink water filter, $420
  4. ZeroWater ExtremeLife faucet mount, $45

Want more options? Look for filters that have been approved by NSF, a not-for-profit product testing and certification company.

3. Radium

Threat Level: High

Not all water is created equal. For decades, residents of southeast Colorado (specifically, the rural towns that stretch east from Pueblo to Lamar) have contended with dangerous radionuclides in their groundwater. These radioactive materials—think: radium and uranium—are naturally present in the Earth’s crust and were tapped into via the deep wells that provide drinking water to the area. (Most major metros, such as Denver, use surface water from reservoirs.) National data shows that, of 50,000 water systems, six of the 10 worst radium levels can be found in the Centennial State. When consumed over extended periods, radium can fracture teeth, lead to birth defects, and increase cancer risk. “No one should have to drink that quality of water,” says Chris Woodka, senior policy and issues manager for the Southeastern Colorado Water Conservancy District.

Arkansas Valley Conduit. Photo courtesy of U.S. Bureau of Reclamation

Fortunately, the main stretch of the Arkansas Valley Conduit, a 130-mile pipeline connecting Pueblo Reservoir to 39 communities, broke ground in late April—after first being authorized in 1962. The first few miles of the project should come online in early 2025; however, it’ll be at least 2031 before the full length is completed. And that’s only if funding can be found to cover the expected $600 million price tag, more than half of which has been secured through a combination of federal dollars and grants and loans from the Colorado Water Conservation Board. “It’s an economically disadvantaged area of the state,” Woodka says. “We have to work very hard to make sure we’re not saddling them with large payments down the road.” In the meantime, CDPHE continues to require public water systems to test for radium and inform people of the results; bottled water, filters, or whole house purification systems can make the drinking water safe while residents continue to wait for their lifeline.

Well Water

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About seven percent of Colorado’s population relies on private well water that can contain naturally occurring minerals such as iron and manganese, which are not health threats, and contaminants such as arsenic, radium, and nitrates, which are. Testing of these wells in mobile home parks was not mandated by the state or through the Safe Drinking Water Act—until last year. That’s when Colorado legislators approved a bill that outlines the creation of a CDPHE-funded water testing program specifically for mobile home parks. It requires site owners to cover the cost of remediation when issues are discovered (grants are available) and provide residents with safe water via filters or another approved method while those fixes are in progress.

4. Microplastics

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In May, the nonprofit Environment Colorado Research & Policy Center released some troubling findings from its study of 16 Front Range bodies of water: Microplastics were present in all of them. The teeny-weeny, smaller-than-a-pencil-tip pieces of plastic wash off our clothes, drift into rivers from landfills, or fall in raindrops. Research is still ongoing, but microplastics have been found to suffocate animals who ingest them. Water treatment plants stop most microplastics from entering our drinking water; still, the minute plastics have been found in people, and plastic waste is generally on the rise in the United States.

Few federal health advisories or regulatory standards exist yet when it comes to microplastics in drinking water. But some efforts are underway: On January 1, for instance, statewide legislation kicked in that phases out single-use plastic bags and single-use polystyrene cups and containers, which should help reduce exposure. “We know enough to know it’s bad,” says Danny Katz, executive director of CoPIRG, a Colorado consumer protection organization that worked on the report. “We are hoping that by identifying that our waterways do have these microplastics, it can shine a spotlight on [the fact] that we do have a problem.”

5. Wildfires

Threat Level: Medium

Wildfires don’t just wreak havoc on our landscapes and our livelihoods. Whether they ignite deep in the forest or closer to urban areas, these blazes can impair the water supply by damaging watersheds, destroying infrastructure, and depositing contaminants that not all utilities are prepared for or have the money to address. The most significant water impacts tend to be short-term issues—though they can extend for up to a decade. To better understand those ramifications, we dug into three key issues created by recent Colorado blazes (most prominently the Marshall fire, which burned through Louisville and Superior at the end of 2021) and how institutions continue to address them.

Cause for Concern:

Louisville found contamination in its post-treatment distribution system after super-heated gases and melted materials from burning homes and structures leeched into the pipes.

Solution: In unburned areas, multiple flushings of the system cleared out the issue within a week. Burn zones took one to four months to flush and test before coming back online. Since the fire, the city has spent close to $1 million on subsequent testing.

Louisville appears to have kept residents safe, but it didn’t charge for water during January, leading to a massive revenue loss. In addition, urban wildfires—which burn things like cars and microwaves—are a relatively new phenomenon, so regional labs or smaller water systems may not even be aware of what chemicals to test for, extending the time it takes to identify and clean out local water systems.

Cause for Concern:

As structures burned in Louisville and Superior, so did the water meters and shut-off valves. Water poured into smoldering foundations, emptying the city’s water storage tanks, which were filled with treated H20.

Solution: At first, Louisville flipped on an emergency interconnect to allow additional water to flow to Superior after its neighbor’s water treatment plant went offline. But firefighters still needed more to fight the wildfire, so they opened a valve that allowed raw, untreated water to reach the storage tank. (A boil water advisory was immediately sent out, warning residents not to use the water for drinking or bathing and to instead rely on bottled water or the H2O being trucked in by emergency responders.) When the immediate danger was over, the whole system had to be flushed and decontaminated before safe water could flow again.

The decontamination process took up to four months in burned areas, delaying the distribution of clean water. Another reason for the holdup: Regulatory standards for decontaminating a water system after letting raw water in didn’t exist—because it’d never happened before, says Louisville city manager Jeff Durbin. To prevent this issue in the future, remote meters are being installed in rebuilt homes and new neighborhoods and the city is looking into implementing this and other isolation technologies in older homes.

Cause for Concern:

Fire wipes out trees and disturbs the soil, so when snowmelt and rain flow over the affected area, it’s able to pick up higher concentrations of dissolved organic carbon (DOC). This turns the water brown (yuck), but it’s also a treatment problem. Chlorine is the go-to disinfectant, but when it interacts with DOC, the compound can create byproducts that are known to be carcinogenic.

Solution: Thankfully, this didn’t end up being an issue during the Marshall fire, but it was a problem after the 2012 High Park fire west of Fort Collins. The best way to remove DOC is through coagulation—or adding metal salts to the water. The effects of the wildfire could be seen for up to three years.

Coagulation is an added expense for utilities. “Any significant change from what you were expecting year-to-year is going to create issues,” says Fernando Rosario-Ortiz, an environmental engineering professor at University of Colorado Boulder.

This article was originally published in 5280 Health 2024.
Daliah Singer
Daliah Singer
Daliah Singer is an award-winning writer and editor based in Denver. You can find more of her work at daliahsinger.com.