Not all water testing laboratories are the same.
How to Evaluate a Legionella Testing Laboratory in Five Steps
But First Why Does It Matter?
Reliable laboratory data is the foundation of effective remediation, risk communication, and long-term water safety. Selecting the right laboratory helps reduce operational and reputational risk by ensuring decisions are based on accurate, reproducible science.
Independent performance programs help verify technical accuracy, while standardized methods ensure results are consistent and scientifically sound. Strong culture expertise supports the accurate detection of viable bacteria, and robust quality systems reinforce the reliability and defensibility of results. Transparency in reporting ensures that data can be clearly understood and acted upon.
Laboratories that integrate external evaluation, ISO-aligned methods, and culture expertise provide the most reliable and defensible results.
How to Evaluate a Laboratory
When organizations implement a water management program, Legionella testing often becomes a critical component for protecting building occupants and maintaining safe water systems. However, not every Legionella testing laboratory operates with the same level of technical expertise, standardized procedures, or quality oversight.
Selecting the right laboratory means looking beyond factors such as price and turnaround time to evaluate the scientific methods, certifications, and quality systems that support accurate and defensible testing results.
Facilities that rely on water management program testing should ensure that the laboratory they partner with follows recognized standards and maintains strong laboratory practices. The following five steps can help organizations evaluate whether a Legionella testing laboratory has the capabilities needed to provide reliable and meaningful results.
Evaluate the Laboratory's Quality Assurance Practices
Quality assurance is a fundamental requirement of laboratory operations and is defined within the ISO/IEC 17025 standard, which serves as the foundation for laboratory accreditation. These systems are not optional and must be implemented to ensure competence, consistency, and the validity of results.
Effective quality systems include documented procedures, internal quality controls, equipment calibration, and ongoing staff training. Laboratories are required to perform testing according to validated methods while identifying and controlling potential sources of error. These practices ensure that results are accurate, repeatable, and defensible.
ISO 17025 also requires laboratories to monitor the validity of their results through participation in external proficiency testing programs accredited under ISO/IEC 17043. These programs provide independent verification that a laboratory can produce accurate results under standardized conditions.
When evaluating a laboratory, organizations should assess whether ISO 17025 accreditation is current, how quality controls are implemented, what procedures govern calibration and staff competency, and how proficiency testing, chain of custody, and sample handling are managed.
Verify the Testing Standards and Methods Used
Reliable Legionella testing depends on the use of recognized scientific methods and standardized laboratory procedures. One widely used international standard is ISO 11731:2017, which outlines procedures for detecting and enumerating Legionella in water samples using culture-based techniques.
This standard defines how samples are processed, concentrated, cultured, and confirmed, ensuring that testing is performed consistently and according to established microbiological practices. Laboratories that follow validated and internationally recognized methods provide greater confidence that results are scientifically sound and reproducible.
When evaluating a laboratory, it is important to understand which methods are used, whether those methods are included within the laboratory's accredited scope, and how results are reported, including units such as CFU/L, detection limits, and organism identification details
Evaluate the Laboratory's Experience and Testing Capabilities
Culture testing remains one of the most trusted methods for detecting viable Legionella in environmental water samples. Because these organisms can be difficult to isolate and may be present in low concentrations, successful testing requires specialized procedures, appropriate media, and experienced microbiologists.
Laboratories with strong expertise in culture-based testing are better equipped to process complex samples and distinguish Legionella from other microorganisms that may grow during analysis. Proper sample handling and preparation are also critical, as samples often require concentration or treatment prior to testing.
When evaluating a laboratory, it is important to determine whether testing is performed in-house, how samples are processed before culture, and what methods are used to identify and confirm Legionella once detected.
Review of the Laboratory's Participation in the ELITE Program
Participation in external proficiency testing programs is a key indicator of laboratory performance. The Environmental Legionella Isolation Techniques Evaluation (ELITE) Program, developed by the Centers for Disease Control and Prevention, evaluates a laboratory's ability to detect, enumerate, and identify Legionella using culture methods.
Because laboratories are assessed using standardized samples, ELITE participation provides an independent benchmark of technical accuracy. While it does not replace ISO 17043-accredited proficiency testing required under ISO/IEC 17025, it serves as an additional indicator of consistent performance in Legionella testing.
When evaluating a laboratory, organizations may consider whether the lab participates in the ELITE Program, how frequently it is evaluated, and whether performance results can be shared.
Evaluate Reporting Transparency and Communication
In addition to technical capability, laboratories must clearly communicate how testing is performed and how results should be interpreted. Transparent reporting helps organizations understand what results mean within the context of their water management program.
Laboratory reports should include key details such as the testing method used, detection limits, and any relevant limitations or conditions that may affect interpretation. Clear communication is especially important when positive results are detected, enabling organizations to respond quickly and appropriately.
When evaluating a laboratory, it is helpful to review sample reports, understand how urgent results are communicated, and assess whether technical guidance is available to support decision-making.
Our Approach at I-2-I Solutions
At I-2-I Solutions, our approach is built around the same principles used to evaluate high-performing Legionella testing laboratories. We are ISO/IEC 17025 accredited and emphasize independent performance verification through participation in recognized proficiency testing programs, including the CDC ELITE Program and ISO 17043-accredited programs such as those provided by NSI Lab Solutions, which are required to maintain ISO 17025 accreditation. This demonstrates our commitment to nationally recognized standards for laboratory competence and quality management.
Our laboratory practices align with standardized methods such as ISO 11731:2017, supporting accurate and reproducible detection of Legionella in water systems. We perform culture testing in-house, allowing for greater control, consistency, and confidence in identifying viable organisms that pose real risk.
This expertise is supported by structured quality assurance systems and transparent reporting practices, enabling us to deliver accurate, defensible results that organizations can rely on for informed decision-making and long-term water safety.
Practical checklist: what to request from any prospective Laboratory
- ☐ Copy of accreditation certificate(s) and scope (ISO/IEC 17025)
- ☐ List of methods used (ISO 11731:2017 and culture confirmation steps)
- ☐ Sample report with CFU/L, detection limits, and interpretive notes
- ☐ Chain-of-custody procedures and sample handling requirements
- ☐ Proof of ELITE Program participation and dates
- ☐ Evidence of ISO 17043-accredited proficiency testing and recent performance
- ☐ Policies for reporting urgent or actionable results
- ☐ Confirmation that culture testing is performed in-house