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Water Quality FAQs

Do I need a water filter?

Denver Water provides safe, clean drinking water to your home. In Denver Water’s experience, homes built before 1951 are likely to have lead water service lines. The water that we provide to homes and businesses is lead-free, but lead can get into the water as it moves through lead-containing household fixtures, plumbing and water service lines — the pipe that brings water into the home from the main in the street — that are owned by the customer.

The Lead Reduction Program will replace customer-owned lead service lines with copper service lines at no direct charge to the customer. Denver Water is also providing a free water pitcher, filter and replacement filters certified to remove lead to all customers identified in the program.

If you have a water filter or treatment system in your home, be sure to follow the manufacturer’s instructions for proper maintenance.

Is bottled water safer than tap water?

Many bottled water companies use tap water as the source. Currently, bottled water is not as heavily regulated or tested as tap water, which is regulated by the Environmental Protection Agency. Instead bottled water is regulated through the Food and Drug Administration and is considered a food product. Additionally, water utilities are required to release information on their water's quality and bottled water companies are not.

Is it safe to drink hot water from the tap?

No, never drink or use hot water from the tap for consumption or food or beverage preparation. Hot water systems (tanks, boilers) contain metallic parts that corrode over time and contaminate the hot water.

How long can tap water be stored, and how should it be stored?

Cold tap water can be stored for about two weeks if kept sealed, away from light and cold or at least cooled, in a clean, amber or foil-covered glass or hard plastic container.

Where does our water come from?

The sources of Denver's water are primarily runoff from snowmelt high in the Rocky Mountains. Our collection system extends into more than eight counties, including Park, Grand, Jefferson, Summit, Teller, Douglas, Clear Creek and Gilpin counties.

Is the water safe from contamination?

Denver Water has caretakers overseeing its source water, but our watershed is very large and potentially toxic spills or acts of nature, though rare, are possible. When a spill occurs we work with the local authorities and regulatory agencies to remedy the situation before it becomes a problem.

Also, it is highly unlikely that toxic spills in the ground or groundwater could contaminate the drinking water since the treated water system is enclosed.

What chemicals do you put in the water?

During the treatment process aluminum sulfate (alum) and polymer are added to the untreated water. These chemicals bind with foreign matter such as dirt particles and form into large clumps that can be removed during the sedimentation and filtration portion of the treatment. After filtration, fluoride is added as needed to achieve fluoridation guidelines set by the state health department. Finally a disinfectant is added to protect the drinking water from potentially harmful microscopic organisms. All chemicals that are added are certified food grade (safe for use in foods).

Other chemicals added include potassium permanganate, carbon dioxide, lime, caustic soda and fluoride containing compounds. All of the chemicals are certified as food grade or to meet ANSI/NSF 60 Standards for Drinking Water Additives and they meet AWWA standards.

What is in Denver's treated water?

All natural waters contain minerals and some chemicals. The Environmental Protection Agency has identified more than 80 potential contaminants that when present at levels above established limits (maximum contaminant level or MCL) may be a health threat. For more information please view the latest Water Quality Report.

Why does my skin itch after showering in the winter?

Our climate is usually cold and dry during the winter, and we tend to take hotter showers because of it. However, hot water dries the skin. Taking a warm shower instead of a hot one should help.

Why does the water appear blue/green when I fill my white bathtub?

Treated tap water is nearly colorless, and — similar to a clear crystal or raindrops reflecting light to create rainbows — the water in your bathtub can absorb and reflect the different wavelengths in the light we see. A blue or green tint in your bathtub water is typically the result of wavelengths of light from the lightbulbs in the bathroom being absorbed and reflected by the water in the tub. The more water there is in the tub the more noticeable the tint may be. Also, different types of light bulbs can make the water appear different colors.

A less likely scenario is that blue- or green-colored water could be caused by particles from the anode rod in your home's water heater degrading, as it’s designed to do. The anode rod, which protects your water heater from corrosion, is made of metals including aluminum, which can form a green gelatinous material as it degrades. These particles may be especially apparent when draining the water heater. 

Bottom line: A green or blue tint to the water in a white bathtub is completely normal. More color may be seen depending on the kind of lightbulbs in your bathroom and the depth of water in the tub. Denver Water routinely tests its water throughout the distribution system, collecting thousands of samples and conducting thousands of tests every year. 

One good test you can do at home is to fill a clean, clear glass with cold water from the tap and hold it up to a light or the sunshine to see if the water has any color.
 

How can I request water quality related data?

You can initiate a request for water quality related data from the DW GIS Maps and Data Request page. After you register, you can request Watershed/Collection Sampling Locations, Watershed/Collection Testing Data, Distribution System Sampling Locations, and Testing Data, as well as Additional Water Quality Data. DW staff will review the request and contact you.

To know more about how Denver Water is managing water quality from source to tap, open this story map.

How do I treat the water for my fish?

Always use a dechlorinating agent for chloramine.

How can PFAS get into the water supply?

Because PFAS is so widely used, the chemicals can get into the water cycle in a number of ways.

Firefighting foam can seep into groundwater supplies. PFAS-containing products in landfills can break down and the chemicals can leach out of the landfill. When PFAS-containing products — such as cookware, cosmetics or water-resistant clothing — are washed with water, trace amounts of the chemicals can be carried down the drain and into the community’s wastewater system.

How is PFAS in drinking water regulated?

Because the chemicals are in so many products used every day and don’t break down on their own, surveys by the Centers for Disease Control and Prevention show that most people in the United States have been exposed to some PFAS. Current scientific research suggests exposure to high levels of certain PFAS may lead to adverse health outcomes; more research is underway.

At the same time, a spotlight has been put on the water and wastewater industries to remove these widely used chemicals from our environment, even the trace amounts that may appear in the water system.

The Environmental Protection Agency's regulatory approach to PFAS compounds in drinking water has evolved over the years, including a health advisory in 2016 on two kinds of PFAS (called PFOA and PFOS), and a second, interim health advisory in 2022. Learn more about EPA health advisories.

In March 2023, the EPA proposed the first-ever national standard to limit PFAS in drinking water. The proposed standard covered six PFAS compounds, with limits set for PFOA and PFOS, and a combined limit for the other four compounds (PFNA, PFHxS, PFBS and GenX). Learn more here.

The EPA’s proposed PFAS regulation would require public water systems to: 

  • Monitor for six specific PFAS compounds in our drinking water. 
  • Notify the public if the levels of the six regulated PFAS compounds are above EPA’s regulatory limits.
  • Reduce the levels of these six PFAS compounds in drinking water if test results are above the EPA’s regulatory limits. 

At the state level, in 2022 Colorado’s Gov. Jared Polis signed a new law (House Bill 1345) that will gradually restrict the sale of PFAS in consumer products, as well as fluids used in the extraction of oil and gas products, starting as early as 2024.

The new state law will prohibit the sale or distribution in Colorado of products that contain PFAS, such as cosmetics, carpets or rugs, fabric treatments, food packaging and juvenile products. Cookware that contains PFAS will have to carry a label.

What is Denver Water doing about PFAS?

Denver Water is committed to ensuring a clean, safe water supply for our customers that meets or goes beyond state and federal drinking water standards. Our water quality experts have tested for PFAS-related compounds in the source water that comes into our treatment plants and the drinking water that leaves our treatment plants since 2017 and have not detected anything above the Environmental Protection Agency’s proposed regulatory limits.

Also, our water quality experts and scientists have been closely studying the evolving information about these chemicals and preparing for solutions in case future test results are above the EPA’s regulatory limits.

We also have been involved in discussions with legislators, state and local regulators and our sister utilities on how to best find, control, remove and prevent PFAS contamination in water.

Denver Water PFAS testing

Our water quality experts have tested for PFAS-related compounds in the source water that comes into our treatment plants and the drinking water that leaves our treatment plants since 2017 and have not detected anything above the Environmental Protection Agency’s proposed regulatory limits. The results below are sampling results from 2023.

Current laboratory equipment can reliably detect and quantify compounds down to slightly less than 2 parts per trillion in a sample. Below that level, the tiny trace amounts are so small that test results at these extreme detection limits are only estimations.

The Environmental Protection Agency's regulatory approach to PFAS compounds in drinking water has evolved over the years, including a health advisory in 2016 on two kinds of PFAS (called PFOA and PFOS), and a second, interim health advisory in 2022. Learn more about EPA health advisories.

In March 2023, the EPA proposed the first-ever national standard to limit PFAS in drinking water. The proposed standard covered six PFAS compounds, with limits set for PFOA and PFOS, and a combined limit for the other four compounds (PFNA, PFHxS, PFBS and GenX). Learn more here.

The EPA’s proposed PFAS regulation would require public water systems to: 

  • Monitor for these six PFAS compounds in our drinking water. 
  • Notify the public if the levels of the six regulated PFAS compounds are above EPA’s regulatory limits.
  • Reduce the levels of these six PFAS compounds in drinking water if test results are above the EPA’s regulatory limits. 

A review of the EPA’s proposed PFAS regulation indicates the drinking water Denver Water provides to customers tests well below the EPA’s proposed regulatory limits for the six PFAS compounds included in the agency’s draft rule.

Denver Water will continue testing for PFAS as part of our monitoring protocols. We regularly review our treatment processes and adjust these processes as part of our mission to provide a clean, safe, reliable water supply to our customers.

If PFAS test results go above the EPA’s regulatory limits, Denver Water might be required to add new and potentially costly treatment methods or find alternative sources of water — which isn’t always an available option in the water-starved West.  

Note: The symbol “<” means “less than” and “ppt” means “parts per trillion.”
Denver Water’s PFAS test results* compared to the EPA’s proposed PFAS regulation
PFAS compound Marston Treatment Plant, treated water 2023 Moffat Treatment Plant, treated water 2023 Foothills Treatment Plant, treated water 2023 EPA’s proposed laboratory detection limits EPA proposed regulatory limit for drinking water Does Denver Water exceed the proposed regulatory limit?
GenX <1.9 ppt <1.9 ppt <1.9 ppt 5.0 ppt Weighted combined score** = 1.0 No
PFBS <1.9 ppt <1.9 ppt <1.9 ppt 3 ppt
PFHxS <1.9 ppt <1.9 ppt <1.9 ppt 3 ppt
PFNA <1.9 ppt <1.9 ppt <1.9 ppt 4.0 ppt
PFOA <1.9 ppt <1.9 ppt <1.9 ppt 4.0 ppt 4.0 ppt No
PFOS <1.9 ppt <1.9 ppt <1.9 ppt 4.0 ppt 4.0 ppt No

*Test results from first half of 2023.
**The “weighted combined score” is the weighted sum of the test results of four specific PFAS compounds: GenX, PFBS, PFHxS and PFNA. The EPA calls this a Hazard Index and any sum above 1 for a year would be considered a violation of the EPA’s proposed PFAS drinking water regulations. Learn more about the EPA’s proposed PFAS Hazard Index.

Note 1: Denver Water’s 2023 test results in the above chart reflect the detection limits of our laboratory’s capabilities. The EPA’s proposed laboratory detection and reporting limits for PFAS are higher.

Note 2: Denver Water also monitors its water for PFAS-related compounds that are not included in the EPA’s proposed regulations, as well as other nonregulated emerging contaminants. In the summer of 2023, test results of treated water at Marston Treatment Plant indicated a PFAS compound called PFBA at a level of 1.9 parts per trillion, which is at the lower limit of laboratory detection and analysis capabilities. The EPA’s list of compounds in the agency’s proposed PFAS regulation for drinking water doesn’t include PFBA, although that may change in the future. More information about PFBA is available at the EPA’s website.

What can you do about PFAS?

You can help! Learn more about where PFAS is used in our society and about alternative, PFAS-free products that you could use instead. This will not only protect your health, but also reduce the amount of PFAS in circulation.

Several groups are working on lists of PFAS-free consumer goods, including PFAS Central.org.