When Should A Building Be Tested For Legionella?

Let’s talk about legionella testing

Legionella testing is when you take samples of water from your water system to be analysed for legionella. You’ll often hear this referred to as, legionella testing, legionella analysis or legionella sampling.

What is Legionella testing and when might you need to do it?

These are both questions that we are frequently asked. Fortunately, the information is readily available to everyone as the HSE has published guidance on this contained within HSG274 part 2.

So let’s get into it. Legionella testing is when you take samples of water from your water system to be analysed for legionella. You’ll often hear this referred to as, legionella testing, legionella analysis or legionella sampling. In order to determine whether or not you need to have legionella testing carried out on your premises, you will first need a legionella risk assessment. This assessment will help you to understand what risks of legionella are present, allow us to see how many water systems are in the building and therefore how many samples must be taken for a legionella sampling programme to be successful, proportionate or even if it is necessary at all.

In most low risk systems, with no reason to suspect increased risk e.g domestic hot and cold water systems, legionella sampling will not be necessary but a risk assessment still will.

We’ve compiled a short list of common examples of when it is recommended to test for legionella within a building.

• A water system is being treated with biocides and the water is stored or distributed at lower temperatures. Testing should initially be carried out frequently to provide an early warning should there be of loss of control. Testing should then be reviewed and continued until there is confidence in the effectiveness of the regime.

• The limits of a control regime, e.g. temperature, circulation or disinfectant concentrations, are not being consistently achieved. In addition to a thorough review of the system and treatment regimes, weekly testing should be carried out to provide early warning of loss of control. Once the system is proven to be brought back under control via your monitoring/recording of the effectiveness of your preventive maintenance/control scheme, the frequency of testing should be reviewed and likely reduced to reflect the regaining of effective control.

• There is a high-risk area or where there is a population with increased susceptibility, for example within healthcare premises, including care homes.
  Special consideration should be given to: Patients or occupants within healthcare premises, residential or care homes where they are exposed to water systems and a range of potential sources of waterborne infection, eg patient ventilation humidification systems that are not necessarily present in a non healthcare setting.HSG 274 Part 2 - 2.153

• A water system is suspected or identified in a case or outbreak of Legionella.

Additionally, the complexity of the system will need to be taken into account to determine the appropriate number of samples to take. To ensure the samples are representative of the water flowing around the system and not just of the area downstream of the fitting, samples should be taken from separate hot and cold outlets rather than through mixer taps or outlets downstream of TMVs (Thermostatic Mixing Valves) or showers.

Flushing:

This is where the outlet is run for at least two minutes before taking a ‘post sample’. A ‘pre sample’ is what is taken immediately from the outlet without running it first.

In both hot and cold water systems, samples should be taken: If considered necessary by the risk assessment. From areas where the target control parameters are not met (i.e. where disinfectant levels are low or where temperatures are below 50 °C (55 °C in healthcare premises) for HWS (hot water systems) or exceed 20 °C for cold water systems). From areas subject to low usage, stagnation, excess storage capacity, dead legs, excessive heat loss, crossflow from the water system or other anomaly.
HSG 274 Part 2 - 2.122

Recommended temperatures:

Legionella thrives in warm water above 20 °C and below 50 °C. The guidance produced by HSE recommends keeping outlet temperatures for cold water below 20 °C and hot water above 50 °C.

Dead legs:

These are sections of pipework that lead to nowhere. For example, from outlets which have been removed but the pipe work to them still exists. Areas of buildings where water is not used frequently should also be considered as dead legs. Dead legs create areas for water to stagnate and microbial growth to occur.

In cold water systems, samples should also be taken as required: From the point of entry (or nearest outlet) if the water is supplied from a private water supply or where the temperature of the incoming mains supply is above 20 °C from the cold water storage tank or tanks. From the furthest and nearest outlet on each branch of the system (far and near sentinel outlets).
HSG 274 Part 2 - 2.124

In hot water systems, samples should also be taken as required:

From the calorifier hot water outlet and from the base of the calorifier (water heater), if it is safe to do so, as some systems are under considerable pressure. From the furthest and nearest outlet on each branch of a single pipe system (far and near sentinel outlets).

Further Reading:

• Health and Safety Executive  - HSG274 Legionnaires' disease technical guidance
  
  
• British Standards - BS 7592. Sampling for Legionella bacteria in water systems. Code of practice

 

Legionella Sampling Services

Founded in 2001, SMS Environmental is one of the UK's largest providers of full water and air hygiene and treatment services, offering a broad range of water treatment, analytical and environmental services with an emphasis on Legionella Control.

SMS supplies services to over 700 customers throughout the UK in every public and private sector, including housing, education, leisure, healthcare, commercial, defence, prisons, blue light and infrastructure organisations.

For more information on the water hygiene services we have to offer or to book a legionella risk assessment please call 0800 138 21 21 or use the form below.

Parts of the above article have been taken directly from the HSG274 part two guidance and have been written in blockquote as reference.