Knowledge Centre


What methods of Legionella testing are there?


Employers right across the UK should be aware of Legionella and the potential risk to employees if the water supply to buildings, factories or warehouses is not monitored regularly.

Every business will have different facilities available some just a kitchen area and toilets whereas others have showers and other water usages.

Water Sample Testing

There are four circumstances when implementing legionella water sample testing is neccessary, and for each the amount of sampling and how often it should be done differs.

1. When a biocide is used instead of temperature as the primary Legionella control method. Some company’s may decide to drop their hot water temperatures and use a chemical treating system (usually chlorine dioxide or silver copper ions) to control the risk of legionella.

In this case, sampling should be carried out monthly from sentinel outlets and from any potentially problematic areas such as areas identified as low use. Once three consecutive sets of sampling indicate the system is clear, then this sampling can be carried out quarterly. The purpose in this case is initially to determine that the installation of the biocide has been effective, and then to continue to monitor if there are any problems.

2. When control measures are not being achieved, either the temperatures or biocide levels are outside of their recommended ranges. In this case, weekly sampling is recommended until control is re-established.

Samples should be taken from any areas where control parameters are not being met. Legislation specifically recommends that this should be done when cold water supplies are in excess of 20°C, such as during hot summer months.

3. The third method is when there are high-risk areas or population. A high-risk area would be a site with significant storage of water or heavy contamination and a method of generating significant aerosol, such as a jet washer which is supplied water by a large volume tank.

A high-risk population includes the elderly and the sick, so hospitals and care homes may decide to implement sampling. The frequency and extent of this sampling is not specifically defined within the guidance, and the appropriate level of sampling will vary between sites.

An inpatient hospital with oncology and intensive care wards would warrant a more stringent sampling regime than a care home. If you fall into this category, it is best to discuss your specific situation with a competent person like our team here at Euro Environmental to determine what sampling regime would be best for you and your workforce.

4. The fourth situation is if there is an outbreak or a suspected outbreak of Legionella, in which case the investigating HSE officers may request that samples be taken. In this case the investigating officers will determine where samples should be taken, typically this will be any areas they suspect may be the source of the outbreak.

Water Temperature Testing

Ongoing system condition testing and inspections to prevent the likelihood of legionella proliferation should be carried out as a minimum regardless of whether or not samples are being taken.

In this instance, tests should be carried out on a monthly basis by placing a thermometer into the stream of water and the temperatures should be recorded as follows:

The water in cold water outlets should reach the control temperature of ≤20°C within two minutes of opening it. Any deviation should be reported as soon as possible. If there are thermostatic mixing valves fitted on the outlet, the temperature readings should be measured prior.

The water in hot water outlets should reach the control temperature of ≥50°C within a minute of being opened. Any change in this, should be reported. Again, where thermostatic mixing vales are present, the temperature readings should be measured prior to the device suing a surface mounted thermometer. 

There are some environments that require a slight amendment which includes all healthcare environments - they require a hot water outlet temperature of >55°C. 

Cold water storage tanks also require regular inspections. Where cold water storage tanks are present, temperature checks should be carried out every six months and the temperature should be measured to ensure its ≤20°C.

Inspection of the actual tanks condition should be carried out on an annual basis to identify its cleanliness, insulation, for any insects, the lids fit well and other and general operating conditions.

Where calorifiers are present temperatures should be taken every month on the flow and return points. The flow should be achieving temperatures of ≥60° C and the return ≥50° C. In addition to temperature checks yearly blowdowns should be carried out. 

Other Types of Testing

Shower head Descales:

Where showers are present shower heads should be cleaned and descaled every 3 months (or more frequently if required). This can be done by leaving the head to soak in a descaling solution for approximately 5 minutes before washing the solution off thoroughly. If required, the head can be soaked in the solution again.

Infrequently Used Outlet Flushing:

Any outlet which is not used at least once a week is classed as infrequently used. Outlets which fall in this category should be flushed thoroughly for around 5 minutes once a week.

For more information on Legionella testing in your workplace, give us a call to discuss your requirements: 0870 7019170

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