The tap water supplied by the City of Boulder is consistently safe to drink, meeting or exceeding all federal and state regulatory standards set by the Environmental Protection Agency (EPA) and the Colorado Department of Public Health and Environment (CDPHE). The municipal water system undergoes rigorous, continuous monitoring to ensure high water quality before delivery to homes and businesses. While the public supply is safe, the final quality at the tap can sometimes be influenced by the plumbing within individual buildings. This article focuses on the public supply and the processes that ensure its safety.
Boulder’s Water Source and Purification Process
Boulder’s water originates from high-quality sources, primarily relying on snowmelt from alpine headwaters on both sides of the Continental Divide. Approximately two-thirds of the annual supply comes from the Middle and North Boulder Creek watersheds, stored in reservoirs like Barker and Silver Lake. The remaining one-third is sourced from the Upper Colorado River basin via the Colorado-Big Thompson (CBT) and Windy Gap projects. Sourcing water from both the eastern and western slopes of the Rockies provides a resilient supply against weather fluctuations.
The collected source water is treated at either the Betasso or Boulder Reservoir Water Treatment Plants through a multi-step purification process. Initial treatment involves the addition of a coagulant, such as aluminum sulfate, to neutralize the electrical charges of suspended particles. This is followed by flocculation, where gentle mixing encourages these particles to clump into larger masses called “floc.”
The flocculated water then moves to sedimentation basins, or in the case of the Boulder Reservoir plant, Dissolved Air Flotation (DAF) units, to separate the solids. After this initial clearing, the water passes through specialized filters to remove any remaining fine particles. Post-filtration, a controlled amount of chlorine is added for disinfection to eliminate pathogens and maintain a protective residual throughout the distribution system.
A final step is corrosion control, where the city carefully adjusts the water’s alkalinity and pH using calcium hydroxide and carbon dioxide. This process is designed to make the water less corrosive, which helps protect distribution pipes and household plumbing from leaching metals. Additionally, fluoride is added to meet the target concentration of 0.7 milligrams per liter, following health recommendations to reduce tooth decay.
Regulatory Oversight and Quality Reporting
The safety of Boulder’s drinking water is maintained through a comprehensive legal and transparency framework established by state and federal authorities. The EPA sets national standards under the Safe Drinking Water Act, while the CDPHE enforces these rules and prescribes regulations specific to Colorado public water systems. This oversight mandates routine testing and compliance with Maximum Contaminant Levels (MCLs) for a wide range of substances.
The city is required to publish an annual Consumer Confidence Report (CCR), which summarizes the previous year’s water quality testing results. This report details the water source, substances detected, and how those levels compare to regulatory limits. Residents can find the most recent CCR readily available on the City of Boulder’s website.
To ensure compliance, the city’s water utility collects samples at the source, throughout treatment, and within the distribution network. The city monitors for over 450 different water quality substances, including bacteria, inorganic contaminants, and industrial byproducts, going beyond the minimum federal requirements. The large volume of testing, approximately 25,000 individual tests annually, provides a robust dataset confirming consistent water quality.
Key Contaminants and Infrastructure Considerations
A primary concern for any municipal water system involves the potential for lead and copper exposure, regulated by the federal Lead and Copper Rule. While the water is virtually lead-free when it leaves the treatment plants, lead can enter the water from old service lines and household plumbing. Due to consistently low lead concentrations demonstrated over several years, Boulder is on a reduced monitoring schedule, sampling only once every three years.
The city actively manages this risk through its Corrosion Control Program, which reduces the water’s ability to dissolve metals from pipes. Furthermore, the City of Boulder is conducting a service line inventory to meet new federal requirements for identifying potential lead pipes leading to homes. Although initial data suggests no lead service lines exist in the city’s owned infrastructure, residents in homes built before 1956 should verify their private service line material.
Disinfection Byproducts (DBPs) are another class of contaminants that form when the chlorine used for disinfection reacts with naturally occurring organic matter in the source water. The city monitors for two main groups of DBPs: Total Trihalomethanes (TTHMs) and Haloacetic Acids (HAA5). Recent monitoring results show that TTHM and HAA5 levels are well below the federal MCLs, indicating effective management of the chlorination process.
Boulder’s water is naturally soft due to its high-mountain, snowmelt origins, with an average hardness of only 42 milligrams per liter. This low mineral content, particularly of calcium and magnesium, is beneficial for appliances and plumbing, reducing the likelihood of scale buildup. All drinking water contains naturally occurring substances, such as minerals and salts, which do not necessarily pose a health risk.
Personal Filtration and Monitoring
While the municipal water supply is safe, some residents utilize home filtration systems to address aesthetic concerns, such as chlorine taste, or to enhance protection against contaminants from household plumbing. Simple pitcher or refrigerator filters, which typically use activated carbon, are effective at reducing chlorine taste and odor, significantly improving the palatability of the water.
For those with older homes, especially those with plumbing installed before the 1980s, testing the water for lead is a prudent step to ensure safety. The city recommends flushing the cold water tap for thirty seconds to two minutes if the water has been sitting motionless for several hours, which helps clear water that may have picked up metals.
More comprehensive filtration systems, such as reverse osmosis (RO) units, can remove a broader spectrum of contaminants, including heavy metals and dissolved solids, but require regular maintenance. Point-of-use filters, installed directly at the tap, or whole-house systems offer varying levels of water quality enhancement. Home water testing kits are available for residents seeking confirmation of their private water quality, particularly if they are uncertain about the age or material of their home’s internal plumbing.