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Drinking Water Quality


Boulder has implemented a comprehensive water supply water quality monitoring program for over 30 years. Water quality samples are routinely collected from creeks and reservoirs throughout the Boulder Reservoir Watershed and the Boulder Creek Watershed. Water quality is also monitored during the drinking water treatment process, and in the city’s water distribution system for operations and compliance with drinking water regulations.












Water Quality Results

All drinking water, including bottled water, contains substances that do not necessarily pose health risks. The city goes above and beyond regulatory requirements, monitoring for hundreds of water quality substances including basic chemistry (e.g., pH, alkalinity), nutrients, bacteria, sediments, organic chemicals (e.g., disinfection byproducts, pesticides, pharmaceuticals, personal care products, hormones), metals, and radionuclides. The vast majority of these compounds and chemicals are not detected in drinking water.  The city goes above and beyond regulatory requirements, monitoring for more than 450 water quality substances, which is over five times more than the number of substances with regulatory limits.






Annual Drinking Water Quality Reports

Water Hardness


Boulder’s water hardness is generally soft but can change seasonally. The water hardness gauges below show current levels for each water treatment plant (WTP). While customers can receive water from either WTP, those who live in the western portion of the city tend to receive Betasso water, while those in the eastern portion of the city tend to receive Boulder Reservoir WTP water.

                                                                             Water hardness levels at the Betasso and Boulder Reservoir treatment plants are currently on the softer side of the scale at 49 milligrams per Liter and 32 milligrams per liter, respectively.









Water hardness is determined by naturally occurring minerals, including calcium and magnesium. Very hard water can form scale and leave deposits in sinks. When washing with soft water, your hands may still feel slippery even after rinsing away the soap. Some dishwashers and appliances may recommend settings depending on water hardness.


Fluoride is a mineral that is naturally found in air, soil, water, plants and foods. Boulder's water sources contain small amounts of natural fluoride. The City of Boulder also adds fluoride to the drinking water to achieve a target level of 0.7 mg/L, which is based on 2015  federal  and  state guidance. The City of Boulder continues to pay close attention to scientific and regulatory developments and, as always, will comply with all regulatory changes.


Why is fluoride added to drinking water?
The City of Boulder has added fluoride as part of the water treatment process since 1969, when Boulder voters approved a ballot measure to require the addition of fluoride to drinking water to reduce tooth decay. Any changes to the fluoridation ordinance would need to be approved by a community vote. All community members also have the opportunity to discuss fluoride at the City of Boulder's Water Resources Advisory Board meetings.

What are the benefits of adding fluoride to drinking water?
According to the  Centers for Disease Control and Prevention (CDC), fluoridated water strengthens teeth and reduces tooth decay by approximately 25 percent in adults and children. Nearly all public health, dental, and medical organizations and agencies including the CDC, World Health Organization, American Dental Association, American Academy of Pediatrics, and the U.S. Department of Health and Human Services recommend community water fluoridation. The CDC considers drinking water fluoridation one of the ten great public health achievements of the 20th century.


What is the city's process for adding fluoride?
During water treatment, the city adds hydrofluorosilicic acid to increase the amount of fluoride in drinking water to a target level of 0.7 mg/L.


Is there a drinking water standard for fluoride?
The U.S. Environmental Protection Agency (EPA) has set an enforceable drinking water standard for fluoride, also referred to as a Maximum Contaminant Level (MCL) (i.e., the maximum amount allowed in water from public water systems). The fluoride MCL is 4.0 mg/L. EPA also has a secondary, non-regulatory drinking water guideline of 2.0 mg/L set to protect children against cosmetic effects including tooth discoloration and tooth enamel pitting. The level of fluoride in Boulder’s drinking water is nearly six times lower than the MCL. Fluoridating drinking water is not required, but is a recommended public health measure. Under the Safe Drinking Water Act, EPA is prohibited from requiring public water systems to add any substances for preventative health care purposes.


Are there health risks associated with excess levels of fluoride in drinking water?
According to the  EPA , exposure to excessive levels of fluoride over a lifetime may increase the likelihood of bone fractures in adults. Children under the age of nine, who are exposed to prolonged and elevated fluoride levels have an increased likelihood of dental cosmetic effects, such as pitting and discoloration. To protect public health from exposure to excessive levels of fluoride, EPA has established an MCL of 4.0 mg/L, which is nearly six times higher than the amount of fluoride in the city’s drinking water. For more information, see the Other Helpful Resources section, below.


Can I use tap water with fluoride to mix infant formula?
The CDC has published a community water fluoridation website providing information about preparing infant formula with fluoridated tap water. According to the CDC, infant formula may be prepared with fluoridated drinking water. If your baby exclusively drinks infant formula reconstituted with fluoridated water, the CDC notes that your baby may have an increased risk for mild dental fluorosis. To reduce this risk, the CDC recommends mixing the infant formula with low-fluoride bottled water some of the time. Typically, low-fluoride bottled water is labeled as de-ionized, purified, demineralized or distilled.


Other Helpful Resources

If you have additional questions, please call the City of Boulder's Drinking Water Program at 303-441-3200 or use the 'Make a Service Request' form below.


Boulder’s monitoring program

The water processed by Boulder's two water treatment plants is virtually free of lead and copper. These metals are introduced into drinking water mainly from home plumbing where copper pipes and lead solder are commonly found. This is why in 1986 the EPA banned lead solder in all new home plumbing. Since it has been determined that most lead is leached from solder within five years, the systems identified by the U.S. Environmental Protection Agency (EPA) to be at risk are those built between 1982 and 1987. Therefore, only the Boulder sites built or having plumbing changes within this time span are chosen for the monitoring program. Lead levels measured at these taps throughout Boulder are well below the EPA regulatory Action Level and also review the Annual Drinking Water Quality Report.

What the city is doing to reduce lead

Boulder has implemented a Corrosion Control Program that changes the water chemistry to make the water less corrosive.

Most of Boulder's water comes from snowmelt which is naturally low in minerals. Water with a low mineral content is corrosive to pipes. Corrosion control processes at the water treatment plants reduce the tendency for lead and copper to dissolve out of home plumbing. They also help reduce the incidence of "rusty water" due to corrosion of iron pipes.

Corrosion control processes at the Betasso Water Treatment Plant involve the addition of two substances:

  1. Calcium (using calcium hydroxide from naturally occurring limestone) to adjust mineral content
  2. Carbon dioxide to adjust the pH (acid-base balance) of the water. The result is less corrosive water.

The Boulder Reservoir Water Treatment Plant's water has a higher mineral content which is within the alkalinity and pH range needed for corrosion control to match the Betasso treated water.

Additional benefits of the corrosion control program include an anticipated reduction in the failure rate of both city pipes and residential plumbing and a reduction in the metals that are processed by the Wastewater Treatment Plant.

Industrial and commercial water users may want to note these changes and make adjustments as needed.

Chromium 6

Chromium is a metal naturally present in rocks, soil, plants, and animals. A common form of chromium that occurs in water and the environment is chromium-6. Chromium-6 can occur from natural geologic erosion and is also used in some industrial processes. Levels of chromium-6 in the city’s drinking water from both water treatment plants (WTP) are well below public health regulatory limits as shown in the figure below.

Algae Blooms and Cyanotoxins

Cyanobacteria (also referred to as blue-green algae) are bacteria naturally found in most freshwater systems. The city routinely monitors the cyanobacteria levels in the source water reservoirs and levels are low. Some species of cyanobacteria are capable of producing cyanotoxins, which can pose a public health risk if exposed at elevated levels via contact recreation or drinking water. Cyanotoxins have not been detected in the city’s samples.

Customer Water Quality Issues

Chlorine Taste and Odor – The city uses chlorine to disinfect the drinking water. While the city uses the minimum amount necessary to keep drinking water safe, water can have a chlorine taste and odor. Chlorine will dissipate in drinking water if left in an uncovered container in the refrigerator overnight. 

Rusty Water – Rusty brown/orange water can be caused by a main break, main replacement, construction activities, fire hydrant use, in-home plumbing, or hot water tanks. These activities can disrupt the water distribution system releasing iron from the pipe walls. These metals can taste unpleasant and stain laundry, but there are no known associated health risks. Flushing the cold water tap should clear the water. For information on current water repair projects click here.

White or Cloudy Water – The white water is typically caused by small air bubbles, which will dissipate in a few minutes. If the white water is caused by flakes that don’t disappear, this may be caused by a deteriorating dip tube in the property’s hot water heater.

Pink or Black Mildew – Mildew can form in sinks, showers, toilets or areas with stagnant water. Clean fixtures regularly and fix leaks to reduce mildew and mold growth.