Understanding how Legionella results are calculated helps ensure your water safety measures are effective and compliant.
Eurofins Water Hygiene Testing UK follows ISO 11731 to report colony-forming units (cfu) of Legionella in water. Using untreated, heat-treated and acid-treated plates, the total count is based on the single treatment with the highest confirmed result, not an average. Serogroups like L. pneumophila SG1 and SG2–14 are confirmed separately.
Key points:
- Only one treatment plate is used for total Legionella count
- Serogroups are reported by their highest individual counts
- Total count may not equal the sum of serogroups
For a full breakdown of how Legionella counts are calculated and reported, download our Legionella count guide (PDF).
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