Mitigating Public Health Risks During Low-Pressure Events

For professionals in the drinking water sector, whether you are a public health official, a field operator, a treatment plant manager, or a town council member, protecting community public health is the cornerstone of our daily work. Every infrastructure upgrade, daily monitoring check, and emergency response is driven by the commitment to deliver safe, reliable drinking water.

One of the key aspects of operations and maintenance planning is understanding and planning to prevent the potential public health risks of low-pressure events and main breaks. In order to support your response to these sometimes routine but crucial events, the Water Quality Control Division would like to present a review of recent epidemiological research and outline how our policies support your local response.

The Science: Recent CDC Findings on Low Pressure Events

The Centers for Disease Control and Prevention (CDC) recently published a cohort study investigating the health effects of low-pressure events in drinking water distribution systems across the United States. A low-pressure or pressure-loss event is when pressure in the water distribution system drops significantly below the normal operational pressure of 35 psi. For example, system operators may intentionally reduce pressure in the distribution system when they install, replace, or repair water lines. Broken water mains, failed pumping systems, power outages, leaking storage tanks, and high demand, such as fire flow, can cause unplanned pressure loss within part or all of the distribution system. Low pressure can cause drinking water contamination through backflow events, intrusion of groundwater or standing water around distribution pipes, disruption of distribution system biofilms, and other microbial or chemical contamination events leading to increased risk of widespread illness. 

Understanding the data helps us optimize our preventative and emergency response measures. Here are the key takeaways from the study:

• Gastrointestinal Risk: Households exposed to low-pressure events were found to be at a 20% higher risk for highly credible acute gastrointestinal illness (HCGI) compared to unexposed households.
• Respiratory Illness: The study detected no association between low-pressure events exposure and acute respiratory illness (ARI).
• Vulnerable Infrastructure: Event-level characteristics significantly impacted health risks. Households faced a higher risk of HCGI during low-pressure events involving older pipes (49–93 years), smaller pipe diameters (2–6 inches), iron pipes, or pipes submerged in trench water during repair.
• Mitigation Matters: Crucially, the risk of HCGI was higher when utilities did not disinfect the pipes and equipment before returning the water main to service. This highlights that adherence to standard distribution repair practices directly reduces community illness.

Colorado’s Culture of Protection: WQCD Policy and Guidance

At the WQCD, we view properly responding to main breaks and low-pressure events not just as operational hurdles, but as critical public health interventions. To help systems navigate these events, the Division utilizes Drinking Water Program Policy DW-1 and the Pressure Loss and Main Break Response Guidance.

When responding to an acute health threat or pressure loss, WQCD expects systems to follow these core protocols to safeguard public health:

• Swift Communication with the CDPHE: If greater than than 50% of the distribution system or greater than 100 service connections are affected by the low-pressure or no-pressure event, systems are required to notify the department as soon as possible via our 24-hour Incident Reporting Line at 1-877-518-5608. If the pressure loss is less than 50% or 100 service connections, the system can report the event via email to cdphe.wqacutes@state.co.us. See Pressure Loss Main Break Response Guidance for an email and door hanger template that can be used for smaller outages. 
• Swift communication with customers: 
• Outages Without an Advisory: For standard service interruptions that do not trigger a formal advisory, systems must notify all affected customers either verbally or by utilizing door hangers. This notice should inform residents of the expected duration of the outage and instruct them to flush their own plumbing by running cold water taps once service is restored. Be sure to warn customers that system flushing can stir up sediment and cause discolored water, and advise them to temporarily avoid using hot water or washing laundry. 
• Boil or Bottled Water Advisories: If the pressure loss poses an acute health threat that results in a boil or bottled water advisory, the situation requires a formal Tier 1 public notice. This notice must meet strict regulatory standards, and all steps in the process, from issuing the public notice to repairing the cause of the pressure loss and lifting the boil advisory, must be completed while in consultation with WQCD.
• Safe Excavation and Repair: Whenever possible, maintain pressure in the main during the entire repair process to prevent contamination. If pressure is lost, crews must keep the excavated pit water level below the break and plug all pipe openings when unattended.
• Rigorous Disinfection and Flushing: As supported by the CDC study, disinfection is non-negotiable. Crews must disinfect the interior of all repair pipes and fittings with a 1% chlorine solution. Once repaired, the affected areas must be flushed at a minimum velocity of 3 feet per second (ft/sec) until clear, and disinfected following AWWA C651 standards or Department-approved SOPs.
• Bacteriological Verification: Repair work is not complete until the water is proven safe. Systems must conduct bacteriological testing at representative locations. The number of required total coliform samples depends on your system's size and the scope of the outage. If any sample tests positive for total coliform, the flushing and disinfection procedures must be repeated until all results indicate safe conditions.

A water main break tests the resilience of both our infrastructure and our response protocols. By utilizing data-driven practices and adhering to WQCD guidance, operators and municipal leaders can confidently mitigate risks and uphold our shared mission: protecting the health of every community in Colorado.

➽ Kyra Gregory Local Assistance Unit Manager, Acute Drinking Water Team Member 

➽ Chelsea Cotton, P.E. Lead Drinking Water Engineer, Acute Drinking Water Team Lead

PFAS Rule Updates: Extended Deadlines and What They Mean for Colorado Water Systems

The EPA is proposing revisions to the federal PFAS Drinking Water Rule, introducing significant changes that will provide Colorado drinking water systems with more flexibility and time to meet compliance standards. Here is what public water systems need to know about the upcoming changes and how the department is responding to keep Colorado aligned with federal standards.

What is changing for water systems?

Originally, the PFAS Rule required systems to comply with new maximum contaminant levels (MCLs) for six chemicals and a Hazard Index by April 1, 2029. Under the EPA’s proposed revisions announced in May 2026:

• Four chemicals and the Hazard Index may be dropped: The EPA plans to rescind the regulatory requirements for PFHxS, PFNA, HFPO-DA, PFBS, and the Hazard Index mixture.
• More time for PFOA and PFOS: The EPA is proposing a modified exemption process to give eligible water systems up to two additional years to meet PFOA and PFOS MCL requirements, pushing the compliance deadline to 2031. This extension framework is largely driven by the significant capital costs, supply chain constraints, and workforce limitations systems face when designing and installing new treatment facilities.
• Interim measures and public notice: An exemption gives systems more time, but requirements during that extension period are dependent on a system's specific PFOA or PFOS levels: 
• 12 parts per trillion (ppt) and above: If a system’s PFOA or PFOS levels equal or exceed 12 ppt, they must implement at least two interim control measures. These can include public education efforts and operational adjustments, like blending water sources, or providing point-of-use solutions directly to consumers, such as certified pitcher filters.
• Between 4 ppt and less than 12 ppt: If a system's PFOA or PFOS levels are above 4 ppt and less than 12 ppt, the proposed framework does not require them to implement interim control measures during the exemption period.
• Regardless of contamination levels, all exempted systems will be subject to public notice requirements to ensure their communities remain informed while long-term treatment solutions are built.

(Note: Without an approved exemption, suppliers will still be required to meet the original April 1, 2029 deadline).

What is the department doing?

Because the EPA signaled that these revisions would occur after the deadline for states to submit primacy applications, the EPA strongly encouraged states to request an extension. The department officially requested a six-month primacy extension this spring. This is an administrative step that provides us with the necessary time to review the EPA’s proposed changes and ensure Colorado’s exemption process aligns with the new federal framework. This extension does not impact public drinking water systems or alter the department’s enforcement oversight. It simply ensures our regulatory authority remains intact before the federal rule takes full effect in April 2027.

What are the next steps?

We will continue to update systems as the EPA finalizes these revisions. Currently, the department is communicating directly with the EPA regarding these drafts and the practical feasibility of implementing these PFAS exemptions at the state level.

Importantly, the proposed extensions and revisions do not change immediate testing deadlines. Suppliers must still comply with the initial monitoring requirements for the six PFAS chemicals by April 1, 2027. To satisfy this requirement, systems must complete monitoring and report the results of either two or four samples (depending on system size and source water type) per entry point. If a supplier has completed all required initial monitoring, they should check their monitoring schedule and AIMS Tool to ensure initial monitoring results have been accepted and marked complete. 

For more information, visit the department’s PFAS rule webpage, sign up for future PFAS Rule email notifications, or email cdphe_wqcd_DWrules@state.co.us.

➽ Bryan Pilson Technical, Regulatory Implementation and Coordination Unit Manager