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Sources of drinking water include rivers, lakes, streams, ponds, reservoirs, springs and wells. As water travels over the surface of the land or through the ground, it dissolves naturally occurring minerals and, in some cases, radioactive material. It can also pick up substances resulting from human activity and the presence of animals. Contaminants may include the following:

Microbial contaminants

Viruses, bacteria and other microbes that may come from sewage treatment plants, septic systems, agricultural livestock operations and wildlife.

Inorganic contaminants

Salts and metals, which can naturally occur or result from urban stormwater runoff, industrial or domestic wastewater discharges, oil and gas production, mining or farming.

Pesticides and herbicides

Chemical substances resulting from a variety of sources, such as agricultural and urban stormwater runoff, and residential uses.

Organic chemical contaminants

Substances such as synthetic and volatile organic chemicals, which are byproducts of industrial processes and petroleum production, and may come from gas stations, urban stormwater runoff and septic systems.

Radioactive contaminants

Substances that can be naturally occurring or be the result of oil and gas production and mining activities.

Denver Water is committed to delivering safe water to our customers. Lead can get into water as it moves through customer-owned water service lines and household plumbing that contain lead.

Service lines bring water into a home or building from Denver Water’s main delivery pipe in the street. In Denver Water’s experience, homes built prior to 1951 are more likely to have lead service lines. Homes built before 1987 may have lead solder connecting copper pipes in their plumbing. Faucets and fixtures made before 2014 do not meet today’s “lead-free” requirements. Lead exposure can cause serious health problems for all age groups, especially pregnant people and young children.

To address this issue, Denver Water has launched the Lead Reduction Program, which was approved in December 2019 by the Environmental Protection Agency and Colorado Department of Public Health and Environment.

The Lead Reduction Program has five main components:

• Managing our system’s water chemistry, including an increased pH level to reduce the risk of lead getting into drinking water from lead service lines or household plumbing.
• Maintaining (and updating) a publicly accessible inventory of all customer-owned lead service lines in Denver Water’s service area. 
• Providing a free water pitcher and filters that are certified to remove lead to all customers suspected of having a lead service line until their line is replaced, and for six months after. 
• Replacing the entire inventory of lead service lines within our service area with copper lines at no direct charge to the customer. When initially launched, all lead service lines were slated to be removed by 2035. Progress on service line replacements can be viewed on the program dashboard.
• Ongoing communications, outreach and education to reach and engage with the diverse communities we serve.
   

How the program came to be 

Since 1992, as part of the EPA’s Lead and Copper Rule, Denver Water has monitored water quality in homes that have service lines or plumbing that contain lead.

Only once, in 2012, did test results from those homes indicate additional action was needed to protect public health, and Denver Water remains in compliance today. However, Denver Water is still required to implement the best plan to reduce the risk of lead in tap water in homes with lead-containing plumbing or service lines. 

That plan is the Lead Reduction Program, which is now underway. 

If you are concerned about lead, you can request to have your water tested. Denver Water customers can request a free lead test kit online. Information on lead in drinking water, testing and steps to minimize exposure is available from the Safe Drinking Water Hotline at 800-426-4791, on the Environmental Protection Agency's website and on Denver Water's website.

How to minimize your exposure to lead

You share the responsibility of protecting yourself and your family from lead in your home’s plumbing. You can take the following actions to reduce your household’s risk of exposure.

Flush 

If water has not been used in the property for a few hours, such as first thing in the morning or when coming home from work, run cold water from the kitchen or any bathroom faucet for five minutes. You can also run the dishwasher, take a shower or do a load of laundry to help flush water in your home’s internal plumbing before drinking, cooking or preparing infant formula.

Replace old fixtures

Replace faucets and indoor plumbing with “lead-free” components. Faucets and fixtures installed prior to 2014 do not meet today’s requirements for “lead-free” fixtures.

Clean aerators

A faucet aerator is a small screen added to the end of a faucet to mix air with water to reduce the flow of water coming from the faucet. Remove and clean the aerators on your faucets, as they may have trapped particles from your old lead service line.

Maintain filters

Follow the manufacturer’s maintenance schedule for the filtration system you have, including water pitchers, faucet-mounted filters, under-sink filter or refrigerator filters. The results of your water quality test may help to determine if you still wish to continue using a filter. Boiling the water does not remove lead.

You can find instructional videos on flushing and filter use on our Lead Reduction Program page.

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Denver Water has tested for Cryptosporidium (crypto) and giardia in both raw and treated water since the 1980s. Since that time, Denver Water has never detected a viable indication of either in drinking water.

Crypto and giardia are microscopic organisms that, when ingested, can cause diarrhea, cramps, fever and other gastro-intestinal symptoms. Crypto and giardia are usually spread through means other than drinking water. While most people readily recover from the symptoms, crypto and giardia can cause more serious illness in people with compromised immune systems.

The organisms are in many of Colorado’s rivers and streams and are a result of animal waste in the watershed.

At the treatment plants, Denver Water removes crypto and giardia through effective filtration, and giardia is also killed by disinfection.

Raw water is drawn into mixing basins at our treatment plants where we add positively charged coagulant and polymer to bond with the negatively charged particles that are suspended in the water that we want to remove. As the negatively charged particles and the positively charged coagulants are joined together, they form larger particles called floc.

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Over time, the now larger floc particles become heavy enough to settle to the bottom of a basin from which sediment is removed.

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The water is then filtered through layers of filter media made of anthracite coal. As the water moves through the filter media, larger particles get caught in the spaces between the grains of anthracite, and clear water emerges.

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As protection against any bacteria, viruses and other microbes that might remain, disinfectant is added before the water flows into underground reservoirs throughout the distribution system and into your home or business. Denver Water carefully monitors the amount of disinfectant added to maintain quality of the water at the farthest reaches of the system.

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Treatment operators maintain the water’s pH by adding alkaline substances to make the water less corrosive. This helps strengthen an existing coating on the inside of water service lines. The coating reduces the potential for lead to get into the water.

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Some of the terms, abbreviations and symbols contained in this report are unique to the water industry and might not be familiar to all customers. Terms used in the table are explained below.

Action level (AL)

Concentration of a contaminant that, if exceeded, triggers treatment or other requirements that a water system must follow.

Average

Typical value.

Below reporting level (BRL)

Below the reportable level for an analysis or below the lowest reliable level that can be measured.

Compliance value

Single or calculated value used to determine if a regulatory contaminant level is met. Examples of calculated values include average, 90th percentile, running annual average, locational running annual average.

Contaminant

Potentially harmful physical, biological, chemical or radiological substance. 

Formal enforcement action

Escalated action taken by the state (due to the risk to public health, or number or severity of violations) to bring a noncompliant water system back into compliance. 

Health-based violation

Violation of either a maximum contaminant level or treatment technique.

Level 1 assessment

A study of the water system to identify potential problems and determine (if possible) why total coliform bacteria have been found in our water system.

Level 2 assessment

A very detailed study of the water system to identify potential problems and determine (if possible) why an E. coli maximum contaminant level violation has occurred and/or why total coliform bacteria have been found in our water system on multiple occasions.

Locational running annual average (LRAA)

The average of sample results for samples collected at a particular monitoring location during the most recent four calendar quarters.

Maximum contaminant level (MCL)

Highest level of a contaminant allowed in drinking water. MCLs are set as close to the maximum contaminant level goal as feasible using the best available treatment technology.

Maximum contaminant level goal (MCLG)

Level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety.

Maximum residual disinfection level (MRDL)

Highest level of a disinfectant allowed in drinking water. There is convincing evidence that the addition of disinfectant is necessary to control microbial contaminants.

Maximum residual disinfection level goal (MRDLG)

The level of a drinking water disinfectant, below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.

Nephelometric turbidity unit (NTU)

Measure of the clarity or cloudiness of water. Turbidity in excess of 5 NTUs is just noticeable to the typical person.

Non-health-based violation

A violation that is not a maximum contaminant level or treatment technique.

Not applicable (N/A)

Does not apply or not available.

Parts per billion (ppb)

Parts per billion = micrograms per liter (ppb = ug/L). One part per billion corresponds to one minute in 2,000 years or a single penny in $10 million.

Parts per million (ppm)

Parts per million = milligrams per liter (ppm = mg/L). One part per million corresponds to one minute in two years or a single penny in $10,000.

Picocuries per liter (pCi/L)

Measure of radioactivity in water.

Range (R)

Lowest value to the highest value.

Running annual average (RAA)

The average of sample results for samples collected during the most recent four calendar quarters.

Sample size

Number or count of values. (i.e., number of water samples collected).

Secondary maximum contaminant level (SMCL)

Non-enforceable, recommended limits for substances that may affect the taste, odor, color, or other aesthetic qualities of drinking water.

Treatment technique (TT)

Required process intended to reduce the level of a contaminant in drinking water.

Unregulated contaminant monitoring rule five (UCMR5)

The fifth list of unregulated contaminants, created by the Environmental Protection Agency, to be monitored by public water systems. A new list is determined every five years.

Variance and exemptions

Department permission not to meet maximum contaminant level or treatment technique under certain conditions.

Violation

Failure to meet a Colorado primary drinking water regulation.

WTP

Water treatment plant.

Denver Water monitors for the list of regulated parameters below in our treated drinking water. Sample points include entry points to the distribution system from our four treatment plants — Foothills, Marston, Moffat, Northwater — and sites throughout Denver Water’s distribution system. Moffat Treatment Plant is used for backup operations, typically during dry years, and was offline during the 2025 reporting period.

The data tables below include regulated contaminants from page 7 that were monitored for and detected at Foothills Treatment Plant, one entry point to the Denver Water distribution system, in 2025. If a contaminant from page 7 is not displayed in these tables, then it was not detected above the reporting limit at the sample location.

*Secondary standards are non-enforceable guidelines for contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor or color) in drinking water.

Turbidity has no health effects. However, turbidity can interfere with disinfection and provide a medium for microbial growth. Turbidity may indicate the presence of disease-causing organisms. These organisms include bacteria, viruses and parasites that can cause symptoms such as nausea, cramps, diarrhea and associated headaches.

Total organic carbon (TOC) has no health effects. However, total organic carbon provides a medium for the formation of disinfection byproducts including trihalomethanes (TTHMs) and haloacetic acids (HAA5s). Drinking water containing these byproducts in excess of the MCL may lead to adverse health effects, including liver or kidney problems, nervous system effects, and may lead to an increased risk of cancer.

The data tables below include regulated contaminants from above that were monitored for and detected at Foothills Treatment Plant, one entry point to the Denver Water distribution system, in 2025. If a contaminant from above is not displayed in these tables, then it was not detected above the reporting limit at the sample location.

*Secondary standards are non-enforceable guidelines for contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor or color) in drinking water.

Turbidity has no health effects. However, turbidity can interfere with disinfection and provide a medium for microbial growth. Turbidity may indicate the presence of disease-causing organisms. These organisms include bacteria, viruses and parasites that can cause symptoms such as nausea, cramps, diarrhea and associated headaches.

Total organic carbon (TOC) has no health effects. However, total organic carbon provides a medium for the formation of disinfection byproducts including trihalomethanes (TTHMs) and haloacetic acids (HAA5s). Drinking water containing these byproducts in excess of the MCL may lead to adverse health effects, liver or kidney problems, or nervous system effects, and may lead to an increased risk of getting cancer.

The data tables below include regulated contaminants from above that were monitored for and detected at Northwater Treatment Plant, one entry point to the Denver Water distribution system, in 2025. If a contaminant from above is not displayed in these tables, then it was not detected above the reporting limit at the sample location.

*Secondary standards are non-enforceable guidelines for contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor or color) in drinking water.

Turbidity has no health effects. However, turbidity can interfere with disinfection and provide a medium for microbial growth. Turbidity may indicate the presence of disease-causing organisms. These organisms include bacteria, viruses and parasites that can cause symptoms such as nausea, cramps, diarrhea and associated headaches.

Total organic carbon (TOC) has no health effects. However, total organic carbon provides a medium for the formation of disinfection byproducts including trihalomethanes (TTHMs) and haloacetic acids (HAA5s). Drinking water containing these byproducts in excess of the MCL may lead to adverse health effects, liver or kidney problems, or nervous system effects, and may lead to an increased risk of getting cancer.

*Treatment technique requirement: At least 95% of samples per period (month or quarter) must be at least 0.2 ppm.

*Secondary standards are non-enforceable guidelines for contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor or color) in drinking water.

These parameters do not have an EPA MCL or SMCL, but they can clarify the buffering capacity and mineral content of the water. Some applications of these parameters include understanding scale buildup on water fixtures, caring for a home aquarium or brewing beer.

Since 1996, the Environmental Protection Agency, through its Unregulated Contaminant Monitoring Rule, every five years requires water utilities across the country to test for a list of substances that are suspected of being in drinking water but are not currently regulated under the Safe Drinking Water Act. Utilities report their test results to the EPA, which uses the information to learn more about the presence of these substances and decide whether they should be regulated in the future to protect public health.

Denver Water’s 2025 test results were reported to the EPA as required. The data tables below include substances that were detected during Denver Water’s tests and the levels at which they were found.

The American Water Works Association has more information about the rule and the process on its website. Information about the rule also can be found on the EPA’s website, or you can contact the Safe Drinking Water Hotline at 800-426-4791.

In 2023, three treatment plant entry points (Foothills, Marston and Moffat) were tested for PFAS under UCMR5 and were below the minimum reporting levels. In Q3 and Q4 of 2024 and Q1 and Q2 of 2025, Northwater Treatment Plant entry point was tested for PFAS under UCMR5 and was below the minimum reporting levels.