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

Acute team: How does the WQCD help you prepare for and respond to acute incidents?

Back in October, we discussed different types of acute health risks, what they are, how to report them, and how to prepare your water system. Today, we want to introduce the Drinking Water Acute Team at the Water Quality Control Division (WQCD) that responds to and supports public water systems when acute incidents occur.

What is an Acute Health Risk?

Common situations that may pose an acute health risk include:

• Loss of pressure in a distribution system over a large area, such as from main breaks, power outages, or planned construction
• Detection of Escherichia coli (E. coli) in finished water:
• When confirmed by a repeat sample
• Upon first detection if other information suggests the water may be unsafe
• When follow-up E. coli testing is not completed after a positive total coliform result
• Natural disasters that impact treatment, distribution, or source water quality
• Cross connection or backflow incidents that can create contamination
• Other circumstances that may result in contamination of drinking water

Acute Team Process and Response

When WQCD becomes aware of a situation that may pose an acute health risk, it convenes the Acute Team. This team is made up of experienced staff from multiple sections of the Safe Drinking Water Program.

The Acute Team will:

• Contact the impacted public water system to discuss the situation
• Determine whether the situation qualifies as an acute health risk
• Decide if public notification is required and what type and methods are appropriate
• Work with the system to identify the best course of action
• Specify any additional steps needed to eliminate the health risk

All actions are taken in accordance with Colorado’s Primary Drinking Water Regulations and Safe Drinking Water Program Policy 1: Response to Acute Health Threats at Public Water Systems.

Policy 1 helps WQCD protect public health and implement the Colorado Primary Drinking Water Regulations (Regulation 11). Its purpose is to outline the WQCD’s approach to protecting drinking water consumers from acute health risks using methods such as requiring public water systems to quickly notify customers when an acute health hazard exists.

What a typical Acute Team response looks like:

1. Responding to an incident report 

The Acute Team receives a report, often through the CDPHE Incident Reporting Line (1-877-518-5608), and contacts the impacted water system to gather details.

2. Evaluation of gathered information 

 

The Acute Team reviews the information provided and determines the appropriate response, including whether a boil water or bottled water advisory and associated Tier 1 public notice are needed. Reporting an incident does not automatically result in an advisory. For small water outages, please refer to our Pressure Loss Guidance. 

 

3. Steps to resolve the acute health risk

WQCD staff talk through the necessary actions to resolve the health risk with the water system. This may include:

• Public notice and distribution methods
• Repairing impacted portions of the treatment or distribution system
• Disinfecting and flushing the distribution system
• Identifying the number and location of follow-up samples
• Sampling to ensure the water is safe to drink
• Communicating actions taken and results to the WQCD

4. Ongoing Support 

 

We encourage you to rely on the network of associations, non-profits, county, and state partners as you respond to and recover from acute situations: 

 

WQCD: Acute Team remains available for questions and may check in periodically for updates. Additionally, the WQCD can review materials such as draft customer communications and sampling or flushing plans. We also offer support through our close relationship with Technical Assistance providers throughout the state, including but not limited to: WQCD Local Assistance Unit, Colorado Rural Water Association, Rural Communities Assistance Corp, Water Now Alliance, and many others.

CoWARN: The Colorado Water/Wastewater Agency Response Network is a coalition of drinking water and wastewater providers, engineers, technical assistance providers, and other water sector providers. The network aims to provide assistance between members during emergencies that affect your ability to provide drinking water and/or wastewater services to your customers and communities. Membership is free to join and easy to use.

Local Public Health Agencies and Emergency Managers: Working with your local public health agency is crucial to navigate an acute health risk. Many public health agencies have contacts with critical local customers (healthcare facilities, daycares, restaurants, grocery stores, etc.) and can help you coordinate communication and additional requirements for them. Local public health agencies may also support water delivery efforts and activate their emergency response teams. 

 

5. Resolution 

 

Once the water system has completed all required actions, the Acute Team reviews the steps taken and any sampling results. WQCD uses this information to confirm that the acute health risk has been resolved and will lift the boil or bottled water advisory. 

 

Emergency Planning

Public water systems should prepare for the steps in this response process in advance.
 

1. Work with partners: You have partners in a variety of state and local agencies. We highly suggest that you coordinate with them prior to an acute event to ensure fast and efficient emergency response.

•  Establish contact with local authorities, public health organizations, and other local water/wastewater providers. Identify up-to-date contacts and develop a communication plan.
• Reach out to your Local Emergency Manager and Local Emergency Planning Committee to ensure your system is part of the conversation about interdependencies with other critical infrastructure suppliers. Consider attending Local Emergency Planning Committee meetings to review emergency plans and incident command structure for your local response teams.
• Coordinate with your communications team to draft potential notices and make a plan to navigate delivering tier 1 public notices. 

2. Complete emergency management documents: The EPA has extensive drinking water-specific emergency management planning documents, templates, and checklists. Even if you have already completed some of these documents, please review them to ensure acute scenarios are covered.

• Risk and Resilience Assessment and Emergency Response Plan Templates
• Incident Action Checklists
• CDPHE Pressure Loss Response Guidance

3. Ensure you have CoWARN Access: If your system has had a CoWARN membership for decades or if you are a new member, we highly recommend that you log into the new website to ensure that you have the correct login credentials and that you are set up to activate CoWARN when the need arises.

• How to join CoWARN
• Action to take to log into new website and generate system profile
• How to activate CoWARN
• Please sign the updated Mutual Aid Agreement and submit it to the CoWARN admin - kyra.gregory@state.co.us

➽ Chelsea Cotton, Lead Drinking Water Engineer

➽ Kyra Gregory, Local Assistance Unit Manager