Denver Water Quality Report 2026: What’s in Your Tap Water

QUICK SUMMARY:

Overall Rating: Good
Top Contaminants of Concern: Disinfection byproducts (trihalomethanes and haloacetic acids) from chloramine treatment, naturally occurring radionuclides (uranium and radium) from the mountain watershed, and lead leaching from older service lines and premise plumbing
Recommended Filter Type: Catalytic carbon for chloramine and disinfection byproducts, or reverse osmosis for the broadest reduction including uranium and radium — see the best under sink water filters and best reverse osmosis systems guides
Water Hardness: Moderately hard — roughly 48–116 ppm (about 3–7 GPG), averaging near 89 ppm

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Denver Water serves roughly 1.5 million people across the city and surrounding suburbs, drawing nearly all of its supply from mountain snowmelt. According to the utility’s 2025 Water Quality Report, the system met every federal health-based standard, with no health-related violations in the most recent three-year period. That statement is accurate, and it is also incomplete. Federal compliance is a legal threshold, not a measure of how clean the water is.

Here’s what the data actually shows. Denver’s tap water is better than most large US systems on the contaminants people worry about most — PFAS was not detected, system-level lead sits well below the federal action level, and nitrate is barely measurable. The contaminants worth attention are narrower: the byproducts of disinfection, the trace radionuclides that come with Colorado’s geology, and the lead that can enter water inside an older home regardless of how clean the source is.

Where Does Denver Get Its Water?

Denver is almost entirely a surface-water city. Its supply originates as snowpack in the Rocky Mountains and flows into a network of mountain reservoirs — Dillon, Cheesman, Gross, and Strontia Springs among them — fed by the South Platte and Colorado River basins. That raw water is treated at the utility’s facilities, historically Foothills, Marston, and Moffat, with the newer Northwater plant expanding capacity on the north system.

Mountain snowmelt is a relatively clean starting point, carrying little of the agricultural and industrial loading that defines river-fed systems elsewhere. What it does carry is a signature of the rock it moves through. Colorado’s granite and mineralized formations release naturally occurring radionuclides — uranium and radium — and the legacy of historic hard-rock mining adds the possibility of mine-drainage inputs in parts of the watershed. Those facts explain most of what distinguishes Denver’s water from a typical surface supply.

How Denver Disinfects: Chloramine

Denver Water uses chloramine — a longer-lasting combination of chlorine and ammonia — as the residual disinfectant that protects water as it travels through thousands of miles of distribution pipe. Free chlorine is used earlier in treatment, but chloramine is what remains in the water arriving at your tap.

This choice has a direct consequence for what ends up in your glass. Chloramine produces lower concentrations of regulated disinfection byproducts than free chlorine, which is part of why Denver’s measured byproduct levels sit comfortably under federal limits. The trade-off is that chloramine is more chemically stable, which makes it harder to remove. It does not dissipate if you leave a pitcher on the counter, and a basic carbon filter struggles with it. Removing chloramine reliably requires catalytic carbon (a specially processed activated carbon that chemically breaks chloramine apart rather than simply adsorbing it) and adequate contact time. For more on how the two disinfectants behave at the tap, see our guide to chloramine vs chlorine in tap water.

What Contaminants Are in Denver Tap Water?

The table below draws on Denver Water’s 2025 Water Quality Report (results reported through 2024) and the EWG Tap Water Database. One column needs explaining before you read it. The EPA’s Maximum Contaminant Level (MCL) is the legal limit — the number a utility cannot exceed without a violation. The EWG Health Guideline is a stricter, health-based benchmark set at a one-in-one-million lifetime cancer risk. The gap between the two is where most of the meaningful risk lives, because the federal legal limits for several of these contaminants have not been updated in close to twenty years.

Contaminant	Detected Level	EPA MCL	EWG Guideline	Health Concern
Total trihalomethanes (TTHMs)	37.9 ppb	80 ppb	0.15 ppb	Cancer, fetal development
Haloacetic acids (HAA5)	22.9 ppb	60 ppb	0.1 ppb	Cancer, reproductive harm
Uranium	Below 30 ppb limit	30 ppb	—	Kidney toxicity, cancer
Radium (226 + 228)	Below 5 pCi/L limit	5 pCi/L	0.05 pCi/L	Cancer
Nitrate	0.119 ppm	10 ppm	0.14 ppm	Oxygen delivery in infants
Barium	0.0399 ppm	2 ppm	—	Blood pressure, kidney
Fluoride	0.675 ppm	4 ppm	—	Added for dental health
PFOA / PFOS	Not detected	4 ppt	0.09 / 0.3 ppt	Cancer, immune effects

Read the trihalomethanes row carefully. Denver’s measured level — 37.9 ppb — sits under the EPA’s legal ceiling of 80 ppb, so by the federal standard this is compliant water. Measured against the EWG health guideline of 0.15 ppb, the same number comes in at roughly 250 times the guideline. Both figures are true at once. That is precisely the point where regulators and consumers tend to talk past each other.

The disinfection byproducts deserve the most attention because they sit at the highest fraction of their legal limits — trihalomethanes at about 47 percent of the MCL and haloacetic acids at about 38 percent — and because the health endpoint, increased lifetime cancer risk with some evidence of harm to fetal development, is well characterized in the research. These compounds form when chloramine reacts with naturally occurring organic matter from the watershed. They are a feature of the disinfection chemistry, not an industrial spill, which is why they appear in essentially every chloraminated surface system.

Uranium and radium are the contaminants that make Denver distinctive. Both are radionuclides released by the erosion of natural mineral deposits, with possible additional contribution from historic mine drainage in the South Platte watershed. Denver Water monitors combined uranium against the 30 ppb federal limit and combined radium-226 and radium-228 against the 5 pCi/L limit, and recent results sit below both. That claim requires context: EWG sets a far stricter 0.05 pCi/L benchmark for radium based on cancer risk, so trace radium that satisfies the federal rule can still exceed the health-based guideline. The distinction matters when you choose a filter, because the technology that removes radionuclides is not the same as the one that removes chloramine taste.

Two contaminants are worth singling out for being low. Nitrate was detected at 0.119 ppm, roughly one-eightieth of the federal 10 ppm limit — a direct benefit of a protected mountain watershed. PFAS is the other good-news finding: testing at Denver Water’s treatment plant entry points in 2023 and 2024 returned results below laboratory reporting levels, and federal UCMR5 monitoring recorded zero detections of PFOA and PFOS. That is an unusually clean PFAS result for a major US system. For households that still want a margin of safety, our best water filters for PFAS removal guide covers the certified options.

You can review the full contaminant list for your system at the EWG Tap Water Database entry for Denver Water.

The Lead Question in Denver

Lead deserves its own section because it behaves differently from everything else above. The contaminants in the table arrive at the treatment plant or form during treatment. Lead does not — it enters water after treatment, by leaching from lead service lines, lead solder, and brass fixtures inside older buildings. The water leaving Denver’s plants is essentially lead-free; what matters is the plumbing between the water main and your glass.

Denver’s system-wide 90th-percentile lead result was 3.59 ppb in the most recent sampling, well under the federal 15 ppb action level. But a citywide percentile cannot tell you what is happening at your specific tap, and for lead, the tap is the only measurement that counts. Lead service lines were common in connections installed before the 1950s, and lead solder remained legal until 1986.

Denver Water has been unusually active here. Its Lead Reduction Program, launched in 2020, raised the pH of the treated water to make it less corrosive, set a goal of replacing all customer-owned lead service lines, and provides certified water pitchers and replacement filters to affected households until their line is replaced. That program is a genuine strength — and a signal, since a utility does not stand up a multi-year service line replacement effort for a system with no lead pipes. If your home was built before 1986, testing your own water is the only way to know your exposure. Our lead in drinking water guide covers sources, risks, and removal in detail.

Denver Water Hardness

Denver has moderately hard water, and this is a point where the popular numbers go wrong. Some aggregator sites list Denver at 368 ppm and label it “very hard,” but that figure conflates suburban groundwater systems with Denver Water’s own supply. Denver Water’s 2025 report shows hardness sampled across its treatment plants running from about 48 to 116 ppm, averaging near 89 ppm — roughly 3 to 7 grains per gallon (GPG). That places the water in the soft-to-moderately-hard band (USGS classifies 61–120 ppm as moderately hard), which is exactly what you would expect from a mountain-snowmelt source rather than a mineral-rich aquifer.

In practical terms, that level of hardness produces only light scale on fixtures and water heaters and has a modest effect on soap lather. It is not severe enough to justify a whole-house softener for most households. If hard-water spotting is a genuine nuisance in your home, our hard water guide and solutions explains the options and when a softener is worth the cost. The more important point for Denver residents is this: direct your filtration budget at the disinfection byproducts, radionuclides, and lead, not at hardness.

Best Water Filters for Denver Residents

Denver’s profile points to a clear priority order: reduce chloramine and disinfection byproducts first, address lead if you live in an older home, and consider reverse osmosis if naturally occurring uranium and radium are a concern for your household. The three options below are matched to that profile. Each carries third-party certification (WQA or IAPMO) to a specific NSF/ANSI standard — verify the exact model in the certifier’s database before buying, since certification is listed by model, not by brand.

Under Sink: Aquasana Claryum 3-Stage

A catalytic carbon-block under-sink system is the most direct answer to Denver’s dominant problem. The Aquasana Claryum 3-Stage is WQA-certified (the Water Quality Association is an accredited body that certifies to the NSF/ANSI standards) to Standards 42, 53, and 401 — covering chlorine and chloramine taste, lead, and a range of organic compounds, the category that includes the precursors and byproducts of disinfection. Because Denver uses chloramine as its residual disinfectant, the chloramine-reduction certification matters here in a way it would not in a free-chlorine city, and the Standard 53 lead certification covers the contaminant most likely to enter water inside an older Denver home. The system installs at a single tap and delivers a higher flow rate than reverse osmosis.

Two real limitations. First, activated carbon does not reliably remove uranium or radium; if those radionuclides are your priority, this is not the unit to choose. Second, the cartridges are rated for roughly 800 gallons or about six months, and replacements run higher per gallon than a basic carbon filter — budget for that recurring cost. Wirecutter and the WQA certified-product listing both confirm Aquasana’s certification claims, which is more than can be said for many carbon systems marketed with “tested to NSF standards” language but no actual certification.

Buy Direct from Aquasana | Check on Amazon

Reverse Osmosis: Waterdrop G3P800

Reverse osmosis is the strongest match for the radionuclide concern, because it is the only common household technology that addresses uranium and radium along with the disinfection byproducts, lead, and trace metals in one system. The Waterdrop G3P800 holds NSF 58 certification for TDS reduction and NSF 372 certification for lead-free construction. The semipermeable RO membrane is the mechanism that rejects dissolved radionuclides, which is why RO is the standard recommendation where uranium or radium are a documented concern. Its tankless design fits under a standard sink.

The trade-offs are inherent to the technology, not flaws in this model. Reverse osmosis strips minerals along with contaminants, so the water tastes flat to some people, sends a portion of feed water to the drain, and needs an electrical outlet under the sink. One installation note: connect the drain and feed line with compression fittings rather than a self-piercing saddle valve, which an increasing number of local plumbing codes now discourage because of long-term leak risk. Consumer Reports’ testing consistently ranks reverse osmosis highest for breadth of contaminant removal — the reason to accept those trade-offs in a city where naturally occurring radionuclides are part of the geology. Verify the specific reduction claims for any RO model in the NSF database, since not every certified system lists radium or uranium. For comparisons, see our best reverse osmosis systems guide.

Buy Direct from Waterdrop | Check on Amazon

Budget Pitcher: ZeroWater 10-Cup Ready-Pour

For renters and households that want lead protection without installing anything, a pitcher is the practical entry point. The ZeroWater 10-Cup uses a five-stage filter and is IAPMO-certified to NSF/ANSI 53 for both lead and chromium reduction (chromium is a health-effects contaminant, so it falls under Standard 53 rather than the aesthetic Standard 42) — which makes it a reasonable hedge for an older Denver home awaiting service-line replacement. Its included total-dissolved-solids meter lets you see when the filter is exhausted rather than guessing from the calendar.

Two real limitations. First, a pitcher’s contact time and capacity are far lower than an under-sink system, so the filter exhausts quickly — often within 20 to 40 gallons in water with any mineral content, and Denver’s moderate hardness will shorten filter life accordingly. Second, the ion-exchange media strips nearly all dissolved solids, which leaves the water tasting flat or faintly metallic to some people; if your household will not drink it, the protection is theoretical. For other pitcher options, see our best water filter pitchers guide.

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How to Test Your Denver Tap Water

Denver Water’s annual report is a system-wide average measured at the treatment plant and across the distribution network. It is the right tool for understanding the source water, and the wrong tool for understanding your specific tap — especially for lead, which forms inside your own plumbing and varies sharply from one address to the next.

A certified home test closes that gap. For a broad screen, Tap Score (run by SimpleLab) sends samples to accredited laboratories and returns results you can read against the same EPA and health benchmarks used above. If you live in a home built before 1986, or your block is on Denver Water’s lead service line replacement list, a lead-specific test is the single most useful measurement you can take. Our how to test your water at home guide explains the options and what the results mean.

Get a Tap Score Test

Frequently Asked Questions

Is Denver tap water safe to drink?

Denver tap water meets all current EPA drinking water standards and recorded no health-based violations in the most recent three-year period. PFAS was not detected, and lead at the system level sits well below the federal action level. “Compliant” is not the same as “free of all contaminants” — disinfection byproducts and trace radionuclides exceed stricter health-based guidelines — but Denver’s water is cleaner than most large US systems on the contaminants consumers worry about most.

Does Denver water have PFAS?

No. Denver Water’s testing at its treatment plant entry points in 2023 and 2024 returned PFAS results below laboratory reporting levels, and federal UCMR5 monitoring recorded zero detections of PFOA and PFOS across the samples taken. A protected mountain-snowmelt watershed with little industrial input is the likely reason. This is an unusually clean PFAS result for a major metropolitan water system.

How hard is Denver water?

Denver water is moderately hard. Denver Water’s own sampling shows hardness running from about 48 to 116 ppm (roughly 3 to 7 grains per gallon), averaging near 89 ppm — soft to moderately hard on the USGS scale. Some aggregator sites cite a much higher “very hard” figure, but that number conflates separate suburban groundwater systems with Denver Water’s snowmelt supply. A whole-house softener is generally unnecessary.

Do I need a water filter in Denver?

For most homes, a catalytic carbon under-sink filter certified to NSF/ANSI 42, 53, and 401 addresses the city’s main issues: chloramine, disinfection byproducts, and lead from older plumbing. If naturally occurring uranium or radium concerns you, a reverse osmosis system certified to NSF/ANSI 58 is the broader solution. Renters and budget-conscious households can start with an IAPMO-certified (NSF/ANSI 53) lead-certified pitcher.

Sources Cited

EWG Tap Water Database — Denver Water Board (PWSID CO0116001): https://www.ewg.org/tapwater/system.php?pws=CO0116001
Denver Water, 2025 Water Quality Report (data reported through 2024): https://www.denverwater.org/your-water/water-quality/water-quality-reports
Denver Water, Lead Reduction Program: https://www.denverwater.org/your-water/water-quality/lead
US EPA, National Primary Drinking Water Regulations (MCLs for trihalomethanes, haloacetic acids, uranium, radium, lead)
US EPA, Fifth Unregulated Contaminant Monitoring Rule (UCMR5) PFAS results
USGS, Water Hardness classification scale
Consumer Reports, water filter testing

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