Common Legionella Mistakes, Myths and Rumours

Monthly Water Testing & Temperature Monitoring


A common misunderstanding is that water needs to be "tested" monthly.  "Water testing" means taking water samples to be tested by a UKAS accredited testing service.  Water does not need to be regularly tested unless a specific risk is identified.  When the term "monthly testing" is used it refers to the monthly monitoring of water temperatures and not taking water samples.


Regular temperature monitoring is a basic requirement of the HSE's ACOP L8 and should be a part of any Legionella control & prevention regime.  Where water temperatures do not meet the requirements of the ACOP L8 then water testing may be advised or required.

Thermostatic Mixing Valves (TMV)


Another common misunderstanding is that TMV valves need to be "maintained" annually.  This misunderstanding comes from Table 2.1 found in HSG 274 Part 2, "To maintain protection against scald risk, TMVs require regular routine maintenance carried out by competent persons in accordance with the manufacturer’s instructions."  Taken in isolation this statement leads many people to carry out work that may not be required.  Further reading of the ACOP L8 and the Department of Health & Social Cares HTM04-01 confirms that maintenance is only required when the valves performance is dropping or failing.  It is the regular monitoring of TMV valves which includes a failsafe check that is the required preventative measure and not regular maintenance.


It is also a very common misunderstanding that TMV valves need to be fitted to every outlet in public buildings, offices, places of work, care homes, hospitals, etc.  This is simply not the case.  The misunderstanding is due to health & safety advisors, health & safety training companies and even the CQC themselves not being technically competent and understanding relevant guidance.  The only legal requirement to fit a TMV valve is found in part G of the Building Regulations, a TMV valve needs to be fitted to bath in any new build or refurbishment.  Other than the Building Regulations the only guidance given in relation to fitting TMV valves recommends that an assessment of scalding risk verses the risk of infection is carried out by a competent person.  The Department of Health's HTM 04-01 recommends that TMV valves are not fitted to outlets which can be mixed (either manually or automatically).

Showers & Spray Outlets


One basic prevention measures of the ACOP L8 is the cleaning and disinfection of "spray" outlets.  The most common spray outlet is a shower but there are many other types of spray outlets that are often missed by assessors who are not competent or properly qualified for the environment they are assessing.  Spray outlets can be anything from showers, pressure washers, over kitchen sink sprays used for washing or food preparations, fountains, water features, etc... the potential list is endless.  Where a spray outlet (not just a shower) has been identified it needs to be cleaned and disinfected on at least a quarterly basis.  However, these measures are not usually carried out for domestic rented properties.

Cold Water Storage Tanks


Cold water storage tanks are designed to deliver cold water to outlets.  The usual reason for storing cold water is because the mains supply does not meet the peak demand for the building.  But just because it's a tank containing water does not mean it is a cold-water storage tank used to supply water to outlets.


There are many types of storage tank.  Some are used to supply fire sprinkler systems, water heaters, heating only systems, take the expansion of heated water and some do both.  The purpose of the tank needs to be established before any control and prevention measures can be recommended.  To many assessors are misidentifying tanks, recommending inappropriate measures and as a result potentially causing damage to the water system.  For example, a tank that supplies a heating only system will be full of all kinds chemicals such as inhibitors which are designed to keep the system clean and prevent freezing.  Assessors who misidentify the tank then recommend cleaning and disinfection, when the tank is refilled, they do not replace the inhibitors which can cause the heating system to slowly breakdown.


The HSE's ACOP L8 only requires the cleaning and disinfection of cold-water storage tanks if there is a reason to do so.  The reasons include taking water samples which identify the presence of bacteria or a visual inspection identifies a need to clean the tank.  Regular cleaning and disinfection as a preventative measure only needs to be carried in high risk environments such as hospitals.

Business or Group Risk Assessments


There is a growing tendency to issue business or group wide risk assessments.  Legionella risk assessments should be specific to the site being assessed and consider the individual nature of the water system and those who may be affected by it.  It is impossible to issue a single risk assessment that covers multiple sites when assessing the risk from Legionella, even if all the sites in the business are identical the water sources may vary and the environment (including neighbouring sites) and those who may be affected will also vary.  These requirements are found in the HSE's ACOP L8 sections 38 to 41.  When issuing a document that covers multiple sites it can only take the form of a policy statement or guidance document, it cannot replace a site-specific risk assessment.

A New Risk Assessment Every Two Years


A new Legionella Risk Assessment is required at least once every two years.  This is a basic requirement of the HSE's ACOP L8.  Unfortunately many businesses and organisations have been told that you can "role over" or "just review" the risk assessment.  This is not true.  A Legionella Risk Assessment must be regularly reviewed during the period it remains valid for but a new risk assessment is required at least once every two years.  Why? because unlike other risk assessments such as Asbestos which is either there or it is not Legionella bacteria grows and fixtures and fittings may deteriate, tanks may require chlorination or water sources change which could promote bacterial growth.

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