Ten frequently and infrequently asked questions:-

We’ve had a legionellosis risk assessment done and…

Q1. The programme of recommendations is too big/complex/expensive – we just don’t think we can implement it. What shall we do?

Q2. We just don’t believe the risk ratings that have been applied, are they correct?

Q3. We don’t think it is “suitable and sufficient”. Is it?


There is a British Standard (BS.8580:2010) for such risk assessments. Many providers state on their reports that their risk assessment method is based on or complies with the standard. Others even have UKAS accreditation. Even these risk assessments can be sadly lacking, for example because the risk assessor does not understand or apply ALARP in the manner expected by the standard. Generally, the surveying, ie data collection, is of an acceptable quality but its interpretation is often woefully inadequate, leading to a lack of confidence and/or impractical/unaffordable recommendations. In order to address this issue, Water Quality London undertakes reviews of risk assessments, with the provision of a revised action plan as an important output. The review also addresses the issue of “continuous risk assessment” and how to implement it.

We’ve had some water samples tested for Legionella (or Pseudomonas aeruginosa) and…

Q4. We don’t believe the results, are they correct?

Q5. We don’t agree with the interpretation that has been offered us, is it appropriate?


There is a common misconception that water sampling is easy, after all it’s only putting some water in a bottle, isn’t it? Or is it? We are continually being asked to interpret water testing results which have been taken without any strategy in mind prior to the sampling. Unless one knows what question one is trying to answer before taking any samples, it is highly likely that any interpretation we be difficult, unconvincing or just plain wrong. The approach of Water Quality London to answering Q4 and Q5 is to check the circumstances of the sampling, who, how, why, when the samples were taken, review the sample handling, transport, laboratory selected and the results. Thereafter we provide a sampling strategy to the client, which better targets the resources being applied to sampling and testing. There are too many samplers who are very happy for their customer to pursue a seemingly endless cycle of sampling and misapplied disinfection exercises, provided by the sampler’s organisation. This cycle should be broken. We shift the effort from tackling symptoms, to root cause analysis, so that the client can eliminate the cause. Legionella (and Pseudomonas aeruginosa) occur in water systems for a reason, not by chance. Our task is to find that reason.