Naturally forming biofilm and its role in shaping water quality has become increasingly accepted in the drinking water industry.  ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) Guideline 12-2023, the premiere Guideline for managing the risk of Legionellosis associated with building water systems, mentions biofilm 34 times.  The Guideline recognizes the role that biofilm plays in Legionella colonization and persistence within plumbing systems and even describes the plumbing system characteristics that promote biofilm formation, microbial colonization, and Legionella growth.  ASHRAE Standard 514-2023, which expands the scope of risk management to include physical, chemical, and microbial hazards in commercial buildings, mentions biofilm 20 times.

However, when ASHRAE Guideline 12-2023 ASHRAE Standard 188-2021, biofilm is not mentioned at all.  ASHRAE 188 simply adds the following at multiple locations in the Standard: “Informative Note: Recommendations and guidance on the design, maintenance, and operation of building water systems are provided in ASHRAE Guideline 12, Minimizing the Risk of Legionellosis Associated with Building Water Systems”.  It is clear that ASHRAE 188 is indirectly acknowledging the role of biofilm by including this informative note.  Unfortunately, this approach shifts attention away from biofilm and the factors that cause Legionella to persist in water systems to the best methods for monitoring Legionella.  Instead of encouraging plumbing system owners to formulate a Water Management Plan (WMP) that addresses/mitigates underlying concerns and prevents Legionella, ASHRAE 188-2021 chooses the route of monitoring and reacting to issues after they arise.  This makes responding to Legionella positives or outbreaks an uphill battle, especially when remediation efforts are not directed at the underlying source of the issue (biofilm).  In plumbing systems that consistently test negative for Legionella, these bacteria can still establish and proliferate within layers of biofilm.  Negative Legionella tests give a false sense of security to those in charge of plumbing system management and increase the risk of Legionella being released from accumulated biofilm to the bulk water during periods of instability (i.e. construction, periods of stagnation, changes in source water, flow surges, equipment failures, etc.).

So why should I test for biofilm?

In addition to avoiding the false sense of security mentioned above, there are three clear benefits of monitoring for biofilm. First, biofilm monitoring is a reliable way to validate the effectiveness of the current WMP.  If a WMP is not effectively controlling for biofilm throughout the water system, there is no guarantee that it is effectively minimizing Legionella risk—bacteria trapped within biofilm can be released during periods of instability (i.e. construction, high velocity flushing, fluctuations in source water quality).  ASHRAE 188-2021 requires that a WMP be implemented to reduce Legionella risk be validated for its effectiveness.  Although it is not required by the Standard, testing water cultures for Legionella bacteria is considered the most defensible way to validate a WMP.  When this culturing technique is coupled with biofilm monitoring, water system personnel can be assured that their WMP is both defensible and effective, and that it will catch a problem before Legionella is detected. 

The second benefit is that monitoring gives an idea of the extent, severity, and cause of biofilm, which can be used to determine the best approach for biofilm mitigation and Legionella control.  By addressing the conditions within the water system that form biofilm to support Legionella growth and proliferation, you can prevent Legionella from establishing in the plumbing system from the start.  For plumbing systems that have an existing WMP, it is never too late to begin biofilm monitoring and maintenance activities to improve water quality.

Finally, benefits of biofilm assessment and mitigation are not limited to Legionella and WMPs—WQI’s biofilm-focused approach has helped solve a variety of water quality issues in complex plumbing systems, including the following:

• Corrosion and Plumbing Failures, including pipe, fittings and equipment
• Lead Copper Rule exceedances
• Repeat Total Coliform positives
• Excessive Heterotrophic Plate Counts
• Taste, Odor, and Aesthetic issues

The common industry strategy is to respond to these water quality issues as they arise, but often it is not until the second or third instance that a pattern is noticed and investigated.  When a pattern is noticed, system personnel often respond to these issues with general solutions—for example, if copper pipes are experiencing leaks more often than other pipe materials, the operator may replace all copper pipes with pipes of a different material.  This approach is reactive, wasteful, and masks the issue without addressing the underlying cause, which can lead to or worsen other, hidden water quality issues.

The following factors contribute to these common water system issues at different stages of the water system:

• Nutrient Availability (unregulated in drinking water)
• Water Age* and Stagnancy
• Flow Velocities
• Disinfectant Type and Residual*
• Water Temperature*
• Plumbing Materials*
• Cross Connections*
• Accumulation of Biofilm and/or Sediment*

The water supply industry largely accepts that these factors are undesirable in water systems.  The points noted above with an asterisk are described in ASHRAE 12-2023 as “characteristics that can make [water systems] prone to significant biofilm formation, microbial colonization, and Legionella growth.” Understanding these factors and how they impact water quality is only part of the solution; what mitigative actions are needed, where and how often to apply them is crucial to any WMP, and WQI has the testing and expertise to guide clients through this complex process.

Why is biofilm monitoring not a part of current Standards and Guidelines?

One reason that biofilm monitoring is not mentioned in the current Standards and Guidelines is due to the lack of non-invasive testing methods capable of accurately assessing biofilm and difficulty in setting Action Limits for biofilm presence.  This concern can be solved with WQI’s Biofilm Indication Test and Biofilm Activity Test, which are proprietary methods specifically developed to assess biofilm presence, severity, and activity without sampling biofilm directly.  WQI also offers the Legionella Indication Test (LIT) which focuses on biofilm formation in relation to Legionella and waterborne pathogens and validates the efficacy of Water Management Plan efforts.  WQI is CDC ELITE certified for Legionella testing and provides both services as a package. 

Our assessments have helped solve a variety of water quality and corrosion issues in water systems and have helped prevent them from returning.  WQI utilizes biofilm assessments to inform existing Water Management Programs and develop the best maintenance and monitoring practices to address the underlying causes of issues.

WQI’s biofilm-based approach has helped clients from a variety of backgrounds.  Our clients in the hospital and healthcare industry range from a large hospital serving nearly 1,000,000 patients a year to a small, 25-bed community hospital experiencing accelerated corrosion issues.  At a major pharmaceutical manufacturing facility, our approach helped reduce corrosion issues and reveal the underlying cause of repeat Legionella positives throughout the plumbing system.  Regardless of the complexities of each water system, our approach has been successful in determining the best course of action to improve water quality in plumbing systems.  To learn more about our success stories, please read our upcoming series of plumbing system case studies.

The industry already acknowledges the role biofilm plays in water quality within plumbing systems.  WQI’s biofilm monitoring and mitigation techniques help bridge the gap between understanding and application.  Our data inform effective responses to biofilm and enhance Water Management Plans.