Deep Dive into Water Disinfection: Keeping Water Safe

Colorado requires all public drinking water systems to have continuous chemical disinfection, except for two suppliers that meet strict standards to retain disinfection waivers and hand-pumped wells at campgrounds. Continuous disinfection is part of a multi-barrier approach to ensuring safe drinking water is available to your consumers.  

Disinfection of drinking water inactivates (i.e., kills or prevents pathogens from replicating) waterborne pathogens, such as bacteria and viruses. The amount of microorganisms needed to cause an infection varies widely between pathogens. The median infectious dose for Salmonella typhosa is 1,000,000 organisms (but can be much less for infants), Hepatitis A virus is between 10-100, and Giardia lamblia and Cryptosporidium are less than 10 organisms. Disinfection does not completely eliminate all living organisms in the water, but does significantly reduce potential acute waterborne disease risk. The pathogen risk reduction is expressed in terms of “log inactivation”. For example, a 3.0 log inactivation value means that 99.9% of microorganisms of interest are inactivated. 

Disinfection can be accomplished using either chemical oxidants, such as free chlorine, chloramines, or ozone, or by photo-inactivation with ultraviolet light. Most Colorado water systems use free chlorine as their main disinfectant. Disinfection with chlorine or chloramines provides a persistent disinfectant residual in the distribution system. This disinfectant residual can provide defense against harmful organisms that enter the distribution system through backflow events, pipeline leaks, low pressure events, or other contamination pathways. 

Regulation 11: Colorado Primary Drinking Water Regulations requires that systems maintain a minimum disinfectant residual concentration of 0.2 mg/L at the entry point and 0.2 mg/L in the distribution system. These two requirements are the same for groundwater (GW), groundwater under the direct influence of surface water (GWUDI), and surface water (SW) systems. Each source type has additional disinfection requirements outlined below: 

• GW sources are considered protected groundwater and are expected to have limited or no pathogens. GW systems must comply with the Groundwater Rule through either triggered source water monitoring in the event of a total coliform positive sample or by certifying that the GW treatment process always provides 4-log (99.99%) inactivation of viruses. 
• GWUDI and SW sources likely have pathogen sources in the water (e.g., beavers, point discharges). Pathogenic organisms are expected and GWUDI/SW systems must meet pathogen log removal/inactivation requirements in the Surface Water Treatment Rule (SWTR). The required treatment is based on three target pathogens:
• Cryptosporidium: 2-log (99%) removal. 
• Higher levels may be required based on LT2 source water monitoring.
• Giardia lamblia: 3-log (99.9%) removal/inactivation.
• Viruses: 4-log (99.99%) removal/inactivation. 

For SW/GWUDI systems: filtration and disinfection are two complementary critical barriers for protecting public health. Drinking Water Policy 4 outlines the removal credits for various filtration types (e.g., conventional filtration, direct filtration). The disinfection treatment must be designed and operated to provide any remaining log inactivation required in the SWTR. These processes work together to ensure that drinking water is safe for the public. 

Next time, we will discuss disinfection log inactivation and the critical parameters for design and compliance demonstration. 

Below are some resources that will give more specific information about the requirements outlined above. If you have questions, please contact Melanie Criswell at melanie.criswell@state.co.us. 

Resources

• Quick guide: Disinfectant residual 
• Quick guide: Minimum disinfection for groundwater 
• Drinking Water Policy 4 (DW004): Surface water treatment rule performance assessment, proper operation and fostering improved operations
• ​Drinking Water Policy 4 - Policy guidance
• Additional information about disinfection is available at the division's Revised Total Coliform Website

➽ Melanie Criswell - Lead Service Line, Corrosion, and Emerging Contaminants Engineer

Thank you to Colorado’s Certified Operators

To Colorado’s Certified Operators: Thank You for What You Do

From all of us on the staff of Colorado’s Water and Wastewater Facility Operators Certification program, we want to take a moment to speak directly to you – the certified operators who keep Colorado’s water systems running safely, reliably, and with professionalism every single day. 

Quite simply: what you do matters, and it matters a lot.

Every time a community turns on the tap expecting clean, safe drinking water or flushes a toilet without a second thought, it’s because of your expertise. Behind the scenes, often unnoticed and sometimes underappreciated, you protect public health and safeguard the environment across our beautiful state. Colorado’s quality of life depends on you.

A Profession Built on Skill, Commitment, and Trust

Water and wastewater operations are not “just jobs.” They are professions that demand technical knowledge, sound judgment, adaptability, and a deep sense of responsibility. From managing complex treatment processes and regulatory requirements to responding to emergencies at all hours, operators are asked to do more with less and to do it flawlessly. 

Obtaining certification isn’t easy, and it isn’t meant to be. It represents your commitment to learning, accountability, and excellence. When you earn and maintain your certification, you demonstrate to your community, your employer, and your peers that you are a trusted professional. We see the effort that goes into studying, testing, continuing education, and staying current in a field that is constantly evolving. 

Showing Up When It Counts

Whether you work for a large utility on the Front Range or a small system in a rural mountain or plains town, your role is critical. During wildfires, floods, droughts, freezes, power outages, and equipment failures, operators are among the first to respond and often the last to leave. You show up when conditions are difficult, when systems are stressed, and when communities need stability the most.

In recent years especially, operators have navigated staffing shortages, aging infrastructure, tightening regulations, and increasing public expectations. Through it all, you’ve kept systems compliant and water safe. That resilience does not go unnoticed. 

More than Compliance

While regulations and certifications are part of the job, the heart of this profession goes beyond compliance. It’s about stewardship – of water resources, public health, and future generations. It’s about pride in doing work that truly serves people.

We also recognize that many of you mentor new operators, share knowledge across systems, and contribute to a culture of professionalism in Colorado’s water sector. That willingness to teach, learn, and support one another strengthens the entire industry. 

Our Commitment to You

As a program, we see our role as partners in your success. Our goal is to support a fair and credible certification process that upholds high standards while acknowledging the realities of the work you do. We continually work to improve guidance, communication, and outreach, as a strong operator workforce is essential to the strength of our water systems. 

Your feedback matters to us. Your experience in the field helps shape how we do our work, and we value the dialogue we have with operators across the state. 

Operator Certification Program staff can be reached at (719) 225-7339, info@coloradocwp.com, cdphe.facilityoperator@state.co.us, or cdphe.wwfocb@state.co.us. 

You can also find everything you need to know about Colorado operator certification using the Operator Resources webpage. 

Thank You

So, to Colorado’s certified water and wastewater operators: thank you for your dedication, your professionalism, and your service. Thank you for the long hours, the problem-solving, the vigilance, and the pride you bring to your work. Thank you for protecting public health and the environment, often without recognition and always with integrity. 

On a personal note, I (Jessica Morgan) also want to share my gratitude as I prepare to step away from public service after nine years, including three and a half years with the Water and Wastewater Facility Operators Certification program. It has been an honor to serve the operator community and to support the important work you do every day. I am deeply grateful for the opportunity to have worked alongside such knowledgeable, committed professionals, and I will carry a lasting appreciation for this field and the people in it. 

We are proud of the operator community in Colorado, and we are grateful to work alongside you – supporting a profession that is as essential as it is honorable. Keep doing what you do. Colorado is better because of it. 💧

➽ Jessica Morgan, Liaison for the Water & Wastewater Operator Certification Board 

➽ Larisa Oringdulph, Program Director of Colorado Certified Water Professionals

Arsenic Water Quality Standards

 

Right now - arsenic is regulated in wastewaters statewide due to water quality standards that were conceived of over 20 years ago. Because arsenic can be quite detrimental to human health and for surface waters that are a source of drinking water, it is important to protect the drinking water supply by adopting protective standards.

Colorado has surface water standards to protect both drinking water (water supply) and fish ingestion. The surface water standard for water supply is 20 nanograms per liter (ng/L). This is quite low, and comparable to the PFAS maximum contaminant levels proposed by EPA (4 nanograms per liter).

The Safe Drinking Water Act regulates arsenic at 10 micrograms per liter (ug/L), or 10,000 nanograms per liter as a maximum contaminant level (or MCL). Also, the practical quantitation limit, or PQL for arsenic currently stands at about 1 micrograms per liter. Having such large discrepancies between the water quality standard, the drinking water MCL, and the PQL creates challenges in implementation of standards within the permitting framework.

The division worked with stakeholders and the commission throughout the 2010s and the early part of this decade to implement statewide temporary modifications because of uncertainty in what the standard should be, and the challenges presented by these discrepancies. While being an interim solution that is unique to Colorado, this solution is only temporary. Each time we extend it, we have to get it approved by our partners at EPA Region 8. Colorado has utilized the temporary modification tool since 2011 (Reg. No. 38.79) to recognize the underlying, use-based standard as a goal while using the level generally deemed to be technologically feasible to set permit limits (i.e., 0.02-3 ug/L). Currently, the arsenic temporary modification is scheduled to expire in 2029. 

As part of the Water Quality Roadmap, the division is currently scoping out what implementation of the protective arsenic standards will look like in the permitting framework. Keep informed of our progress through our quarterly roadmap meetings, which will also offer regular stakeholder input opportunities. The next Roadmap meeting will be held on March 5, 2026.

➽ Tyson Ingels, Watershed & Engineering Program Manager

Coaches' Classroom: Public Notices: Division Tools and Templates to Cover All Your Bases

The public notification rule establishes requirements for public water systems to communicate any problems about the water to anyone using the water they produce. Specifically, problems related to meeting drinking water standards, failing to test the water, or other situations related to protecting the health of consumers all require public notice and must meet the requirements in the Colorado Primary Drinking Water Regulations (Regulation 11).  

Resources
Public Notice Templates are a great tool for efficiently meeting the regulatory requirements. The templates can be generated using our online public notice generator tool. Using the generator tool ensures that your public notice contains the 10 required elements of a public notice, as well as any specific required language.  

Choosing the correct violation category
There are three tiers of public notice:  

• Tier 1 is required for the most immediate potential public health impacts.
• Tier 2 is for situations with potential to have serious effects, such as exceeding a maximum contaminant level.
• Tier 3 is for violations and situations that may not directly impact public health. 

In addition to the tier levels for public notification, public notices may have different language requirements depending on the specific violation. Field-based violations are those that are identified during sanitary survey inspections. When creating a public notice for a field-based violation, you will select the violation category that lists “sanitary survey identified violations - Tier 2 or 3” (see image below). The template will contain instructions and a link to the Public Notice Health Effects Language for Sanitary Survey Tier 2 Violations chart, which provides the language required to be entered for each violation found on your Sanitary Survey findings letter. You will also need to add the description of each violation, the date the violations need to be corrected, and the steps you are taking to correct them in the table provided in the template you generate. Once completed, you are ready to deliver the notices to your customers per the tier requirements. After you distribute the public notice(s), please submit a final copy, along with a certificate of delivery to the drinking water portal.   

Consumer Confidence Reports to Meet Public Notification Requirements
Community public water systems are required to complete a Consumer Confidence Report (CCR) each year.  Under some circumstances, a Tier 3 public notice requirement can be met using the CCR. 

1. The CCR must fall within 1 year of learning of the violation.
2. The CCR must be delivered using a direct delivery method.
3. All 10 public notice elements must be included.

While Tier 2 violations can’t be satisfied with the CCR, all unresolved violations and significant deficiencies are required to be reported on the CCR, this includes those listed on a corrective action plan for a Sanitary Survey deficiency. 

Want to learn more?
If you are interested in learning more about field violations during a sanitary survey and how to complete your public notice requirements, sign up for one of our upcoming free Sanitary Survey Preparation Trainings. If you have more specific questions about health-based violations and PN requirements, join us for our Monitoring and Operating for Regulatory Compliance (MORC) training. All of our training is free and offered in virtual or face-to-face formats.

➽ Angela Green Garcia, Drinking Water Training Specialist

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

Program Manager message: Infrastructure Funding

During the 2020s, we have seen unprecedented federal support for funding drinking water infrastructure. However, it has also been complicated and challenging, and the future is uncertain regarding the continuation of federal funding. Yet it remains quite certain that water infrastructure needs for the next couple of decades will be enormous. The need stems from both replacing aging infrastructure and meeting new federal public health protection requirements, including lead and PFAS, with another major rule coming out in a couple of years to update the Microbial/Disinfection Byproducts (M/DBP) suite of rules.

As we reported in 2022, President Biden signed the $1.2 trillion Infrastructure Investment and Jobs Act (IIJA) into law in 2021. The IIJA appropriated significant funds to the State Revolving Fund Programs (SRF), which is administered by the Co
lorado Water Resources and Power Development Authority, Department of Local Affairs, and CDPHE. The Authority is the grant recipient for the SRF. DOLA evaluates the financial structure of the applicant’s application to the SRFs, and CDPHE manages the technical and compliance aspects of the SRFs. The funding is being allocated in essentially three “buckets,” including general infrastructure, emerging contaminants, and lead service lines. Initially, Colorado was projected to receive approximately $680 million over the five years. However, the actual awards have fluctuated to some degree due to adjustments made in Congress and reallocations of some of the lead money. 

At this point, we are four years in and have one more to go. This funding represents a major opportunity for Colorado. But the need for continued water infrastructure support is enormous, especially considering the new federal drinking water rules mentioned above. There has been talk across the sector about extending the federal infrastructure investment. At the recent annual conference of the Association of State Drinking Water Administrators (ASDWA), a panel regarding funding and finance recommended emphasizing the following points when communicating about water infrastructure needs:

• Positive impact for affordability. With so much pressure on rate payers these days, supporting water infrastructure is one way to support overall economic vitality and help keep water rates affordable. 
• Impact to small, rural communities. These communities tend to struggle most with tackling complicated, expensive infrastructure projects and these funding sources tend to help small, rural communities the most.
• Share responsibility. Federal, state and local governments all share roles and responsibilities for safe water, and infrastructure investments like IIJA demonstrate that commitment. 
• Fundamental societal need. Adequate infrastructure is a cornerstone of safe water which is foundational for the economy and national security.
• Specifically, for restoring SRF funding, the following points were discussed:
• Without the SRFs, loan forgiveness and many great assistance programs that benefit small, rural communities will be lost.
• SRF funding is vital to ensure the efficacy of many state primacy programs, which is a preferred option compared to direct federal implementation.
• The SRFs support water affordability in small, rural communities that cannot afford modern water infrastructure. 
• Commitment to the SRFs is needed because they provide below-market loans, even 0% interest loans and loan forgiveness (like grants), especially to small, rural communities.

We share a collective commitment with local governments to protect public health and ensure safe tap water for all. Sustained infrastructure funding can help us move forward toward that goal. Contact us if your community is interested in pursuing this funding. Thank you.

➽ Ron Falco, P.E., Safe Drinking Water Program Manager

Dear Aqua Answers - Why are unknown service line materials bad?

 Dear Aqua Answers,

I submitted the Lead Service Line Inventory (LSLI) for my water system in October 2024, as required. We were unsure of the construction materials used in some service lines. So, there are some unknowns. Why do I still need to refine my inventory? I heard that unknown line materials are bad. Why?  

Please help. 

Thanks,

Lea D. Line

Dear Lea,

Thank you so much for submitting your initial Lead Service Line Inventory (LSLI) last year. We understand that many systems do not know all the construction materials used in all their service lines. The Lead and Copper Rule Improvements (LCRI) finalized by EPA in 2024 requires ongoing effort to identify service line construction materials and submitting a baseline service line inventory, including connectors, by November 1, 2027. This inventory is different than the initial inventory submitted in 2024. The baseline inventory submittal will establish your system’s baseline for identifying, prioritizing, and replacing lines that contain or may contain lead. 

Under the LCRI, each system must track its progress by calculating a service line replacement rate, which is based on the number of lead, galvanized requiring replacement (GRR), and lead status unknown service lines identified in the baseline inventory. The required Lead Service Line Removal (LSLR) calculation method and required percent removals of lead lines may jeopardize future compliance if you have a high number of unknown service lines that are later confirmed to be non-lead. This lowers the total number of lines in the replacement pool without crediting overall progress in identifying service line materials. This structural flaw risks forcing systems to meet unrealistic replacement rates and/or face non-compliance, even when they have effectively removed all known lead or GRR service lines or ultimately determine all unknown service lines to be non-lead. Customer refusals to allow service line material identification or line removal will also heavily influence system compliance into the 2030s.

This means that unknown service lines are bad for future compliance with LCRI. CDPHE will be communicating with EPA about these concerns and seeking additional flexibility. 

What can you do in the meantime? Make as much progress as possible on your system’s service line (and connector) inventory before the baseline inventory is due on November 1, 2027. Try to reduce the number of unknowns, especially by 2030.

The division continues to support water systems serving up to 15,000 persons by offering technical assistance provided by WSP. The program is currently operating on a wait list, and suppliers can sign up here to be contacted by WSP in the event that the division is able to provide additional funding for the program. Enrolled suppliers can request remote support or hands-on assistance, offered at no cost. The division has selected only one contractor to provide technical assistance to eligible water systems, and it will not reimburse systems for the costs of hiring outside contractors. Waitlisted suppliers should continue to work on their inventories while they await potential additional funding for the program. 

In addition, the division has a team of drinking water coaches available to help you with LSLI project management. Our team can coach your system as you: 

Identify and navigate grant and loan funding for service line identification and replacement 

 Navigate regulatory requirements, including inventory templates, communications tools, public notice and drinking water portal 

Draft and update your LSLI 

If you are interested in working with one of our coaches on your LSLI please fill out a coaching request form, and one of our coaches will reach out to assist you and your team. 

Thank you for your efforts to identify service line materials in your water system. 

Sincerely,

➽ Aqua Answers