Boulder, Colorado, is widely recognized for its high-quality drinking water, which consistently meets or exceeds the stringent standards set by federal and state regulatory bodies. The city’s water utility maintains a proactive approach to monitoring and treatment, ensuring the water delivered to residents is safe for consumption. This commitment is supported by the naturally high quality of its Rocky Mountain source water and a multi-barrier treatment system. For residents and visitors, the tap water is a reliable resource that undergoes continuous, rigorous testing.
Water Source and Infrastructure Overview
Boulder’s water supply originates primarily from high-altitude, protected mountain watersheds, relying on snowmelt from the Continental Divide. Approximately two-thirds of the annual supply comes from the headwaters of North and Middle Boulder Creeks, including storage in Barker Reservoir and the Silver Lake Watershed. The pristine nature of these source areas, which are largely undeveloped, provides raw water that is naturally low in contaminants.
The remaining one-third of the supply is sourced from the Colorado-Big Thompson (CBT) project, which diverts water from the Western Slope of the Rockies. This trans-mountain water travels through a system of tunnels and canals before being stored in the Boulder Reservoir. This dual-source system provides the city with supply resilience against drought or localized events.
The raw water from these distinct sources is routed to one of the city’s two treatment facilities. Water from the mountain sources is directed to the Betasso Water Treatment Plant, while the CBT water from Boulder Reservoir is processed at the 63rd Street Water Treatment Plant.
Treatment Process and Regulatory Assurance
The physical treatment process at both facilities employs a multi-step approach to purify the raw water. The process begins with coagulation, where chemicals like aluminum sulfate are added to neutralize the charge of suspended particles. This is followed by flocculation, which gently mixes the water to cause the microscopic particles to clump together into larger masses called “floc.”
These larger floc particles are then removed through sedimentation or a process called Dissolved Air Flotation (DAF), before the water moves on to filtration. The water passes through layers of sand and gravel, which physically remove any remaining small particles, turbidity, and most microorganisms. Finally, a disinfectant, typically chlorine, is added to eliminate any remaining pathogens and maintain a protective residual as the water travels through the distribution system.
The city implements a corrosion control program to protect the quality of the water as it moves through pipes. Calcium hydroxide (lime) and carbon dioxide are added to the filtered water to adjust the alkalinity and pH, making the water less corrosive to the metal plumbing. This treatment minimizes the potential for metals, such as lead or copper, to leach from household pipes and fixtures into the drinking water.
Regulatory oversight ensures the system remains compliant with the federal Safe Drinking Water Act (SDWA), monitored by the Environmental Protection Agency (EPA) and the Colorado Department of Public Health and Environment (CDPHE). The city’s utility tests for hundreds of substances, including specific contaminants, bacteria, and disinfection byproducts. Compliance is determined by ensuring that detected contaminant levels remain below the established Maximum Contaminant Levels (MCLs).
Addressing Aesthetic and Localized Safety Concerns
While the treated water leaving the plants is of high quality, localized issues can sometimes affect the water that reaches the tap. A frequent question involves the risk of lead exposure, which does not originate from the city’s water mains or treatment process. The City of Boulder recently completed a comprehensive inventory and confirmed that there are no lead service lines within its public water system.
However, lead exposure remains a possibility in older homes due to internal plumbing, such as brass fixtures or lead solder used before the 1986 ban. The city’s corrosion control is designed to mitigate this risk by coating the inside of pipes. Residents can take simple steps for added safety, such as running the cold water tap for a few minutes each morning or after a long period of inactivity to flush out any water that may have been sitting in contact with household plumbing.
Aesthetic factors, like taste and hardness, also influence the perception of water quality. Boulder’s water is classified as soft, with an average hardness measurement of approximately 42 milligrams per liter. This low mineral content means less scale buildup in appliances compared to communities with harder water.
Occasionally, residents may notice a faint chlorine taste or odor, which is the necessary residual disinfectant doing its job. This is a normal result of the disinfection process that keeps the water safe from bacterial contamination. Placing a pitcher of tap water in the refrigerator overnight allows the chlorine to dissipate naturally, which can improve the taste.
How to Review Official Water Quality Reports
The most direct way to verify the quality of Boulder’s tap water is by reviewing the official annual Consumer Confidence Report (CCR). The City of Boulder Water Utility publishes this report every year, and it is easily accessible on the city’s website. This document is mandated by the EPA and provides a detailed snapshot of the previous year’s water testing results.
The CCR lists all regulated contaminants that were detected and compares the measured levels to the federal MCLs. When reviewing the report, look for the columns detailing the “Highest Detected Level” and the “MCL” to see how closely the water adheres to the safety standards. The report also includes information about the water source, the treatment process, and any compliance violations.