Knowledge Centre


Legionella Compliance - The Responsible Persons Guide


Those that work in your business be it in a factory, warehouse healthcare or office environment could be at risk if it has a water system that offers the right environmental conditions for legionella bacteria growth.

There is a higher risk of legionella if your water system has a temperature between 20–45 °C and stores / re-circulates water.

Other factors to be wary of are if your water system create or spreads breathable droplets or contains a source of nutrients for a growing organism including rust, sledge, scale, biofilms or other organic matter.

The potentially fatal Legionnaires Disease is a risk to the entire workforce, however there are several people who the disease poses a higher risk to, these include:

  • Those over 45 years of age

  • Smokers and heavy drinkers

  • The elderly and infirm

  • Those suffering from chronic respiratory or kidney disease

  • Those with impaired immune systems

If any employees fall within these categories, they should be assessed more frequently than others.

Testing to comply with regulations.

Regular monitoring for the potential of Legionella is vitally important and must follow the two main pieces of legislation which are the Health and Safety at Work Act (1974) and the Control of Substances Hazardous to Health Regulation (1994).Organisations that fail to comply with both regulations may be prosecuted should an employee become ill.

Employers have a duty of care under the health and safety at work act to protect their employees and any one visiting the working environment. 

Risk assessing to avoid the risks of Legionella. 

Regular monitoring of your water system(s) is paramount. If someone has contracted Legionnaires, it can spread to others as it is very contagious.

Carrying out a risk assessment is the starting point to ensure you meet legal compliance, it is highly recommended that you appoint an external specialist to perform this task as it will form the foundation of your ongoing control scheme.

The risk assessment should include details relating to the following:

  • Management responsibilities, including the name of the competent person

  • Competence and training of key personnel

  • Details of any identified potential risk sources

  • Any means of preventing the risk or controls in place to control risks

  • Monitoring, inspection and maintenance procedures

  • Water system drawings and a list of all water related assets

  • Details of the ongoing control scheme

  • Identification of the sentinel outlets

The industry precedent is that Legionella risk assessments are reviewed at least every two years. However, there are certain situations when an assessment is required sooner by law:

  • When the site’s population falls within the high-risk category – for example the elderly or those with an impaired immune system

  • When changes are made to the water system, pipework or assets

  • When the water system has had a change of use

  • When new regulations are published with new recommendations

  • When the current ongoing control scheme monitoring and management processes are no longer proving effective

  • When a Legionella outbreak is suspected, or positive samples are recorded

Ongoing control scheme legionella testing

The risk assessment will identify what needs testing and inspecting on a regular basis as part of an ongoing control scheme. The aim of the control scheme is to manage the risk from proliferation of Legionella bacteria in your water system(s).

The schedule of your ongoing control scheme will vary depending on what type of water systems you have in place. In general you will need to carry out tests or risk reducing actions on a minimum monthly frequency and these will typically cover the following items:

  • Flushing of infrequently used outlets

  • Temperatures checks of water heaters, calorifiers and sentinel outlets

  • Calorifier blow downs

  • Showerhead and outlet descales

  • Cold water storage tank inspections

A control scheme logbook record should be maintained to demonstrate that you are adequately managing the risk posed by Legionella. A template example of a logbook system can be downloaded from the download section of our knowledge centre.

What temperatures should my water systems be?

In all buildings, healthcare or non-healthcare sites cold water temperatures should be below 20°C within two minutes of opening the outlet. Stored water temperatures in tanks should also be below 20°C.

Hot water temperatures are a bit more complicated. In a non-healthcare building, hot water should be dispensed from an outlet at 50°C within one minute. If you have a large hot water heater (Calorifier), this should always operate above 60°C, if your hot water system is circulating, the return line should also be above 50°C.

In healthcare sites, this is slightly different. The Calorifier flow and return temperatures should both be the same as in a non-healthcare building, but hot water should reach any outlet at 55°C.

Not all water heaters are bound by the 60°C rule though, point of use water heaters (small water heaters with less than 15L in volume) and combination storage water heaters (water heaters with an internal cold-water storage tank on top of the unit) only need to operate between 50-60°C. (55°C in healthcare).

What outlet points need temperature measurements?

Sentinel outlets should be monitored monthly, and a representative selection of other outlets on a rotational basis over a defined period.

What does this mean for you and your business?

Sentinels are those outlets which are closest and furthest from a source of water. You can have sentinels for different types of water you have on site, so mains water sentinels, tanked water sentinels (if you have cold water storage tanks) and hot water sentinels. You might think that you would have two sentinels for each, closest and furthest, but this is not necessarily the case, it depends how your water systems are laid out.

What about representative outlets, what outlets need to be covered, and over what ‘defined period’?  

Industry standards state that you should check the temperatures of all of your non-sentinel outlets over the course of a year, assessing around 10% of your non-sentinel taps each month, so that all are covered by the end of the year.

You should also check the operating temperature and return temperatures (if they have return lines) of your calorifiers every month. The guidance also says you should check subordinate loop temperatures quarterly. This is generally only applicable in larger buildings. A subordinate loop is a separate hot water circulating loop that branches off from the main circulating system.

If you have a larger building to consider, you should check your pipework schematics to see if you have any subordinate loops present.

How often do temperatures need monitoring?

  • Most temperatures need checking monthly. You should check your sentinels, Calorifier flow & return and some of your representative outlets every month.

  • Subordinate loops should be checked quarterly.

  • Cold water storage tanks should have temperatures checked annually, in the middle of summer.

What type of thermometer should be used? 

The only specific requirement is that the thermometer must be calibrated. Your thermometer should be calibrated every year, if your thermometer has not been calibrated, the temperatures taken using it cannot be used as evidence in court, and that is what your log book is there for, it’s your due diligence defence if the worst should happen. 

You should also use a thermometer that is suitable for the task. If you have a Calorifier you need to record flow and return temperatures from, or outlets fitted with TMVs (thermostatic mixing valves), you will need a thermometer with a contact probe, so you can take pipework readings.

What is the correct way of taking a temperature reading?

This depends where you are taking the temperature from, they all vary slightly: 

  1. When taking the temperature from a cold tap you should immerse the probe under the stream of water. You should leave the water to run for two minutes and record the temperature.

    If the temperature levels off before two minutes, or ‘stabilises’, you can record the temperature at that time. You don’t need to wait the full two minutes if the temperature stops changing.

  1. When taking the temperature from a hot tap without a TMV you should immerse the probe under the stream of water. You should leave the water to run for a minute and record the temperature. If the temperature levels off before the one minute is up, or ‘stabilises’, you can record the temperature at that time. You don’t need to wait the full minute if the temperature stops changing.

  1. When taking the temperature from a hot tap with a TMV you should run the tap and push the contact probe thermometer to a piece of uninsulated, unpainted pipework prior to the TMV. If using an infrared thermometer, put a piece of black matt tape on the hot pipe before the TMV and direct the beam onto that.

    You should leave the water to run for one minute and record the temperature. If the temperature levels off before the minute, or ‘stabilises’, you can record the temperature at that time. You don’t need to wait the full minute if the temperature stops changing.

  1. When taking the flow temperature from a Calorifier you should push the contact thermometer to a piece of uninsulated and unpainted pipework. If using an infrared thermometer, put a piece of black matt tape onto the pipe. Hold the probe there until the temperature stabilises and record. When taking the return temperature, follow the procedure for checking the flow, but try to take the temperature from the return pipe before the circulation pump, as these can generate a lot of heat which can artificially raise the return temperature.

  1. When taking the temperatures from a cold-water storage tank you should first immerse the probe in the stored water within the tank, ideally as far from the inlet valve as possible. Record this temperature, then run the inlet valve and immerse the probe under the stream of water. Record the temperature after 2 minutes or after the temperature stabilises, which ever happens first. You should check the temperatures this way round, as running the inlet valve for two minutes can drop the stored water temperature in the tank, particularly in smaller tanks.

What action should be taken if the temperature is not in the ideal range?

This is where it gets complicated! This depends greatly on the temperature you are taking, if its from a tank, the mains, if it’s hot and by how much the temperature is out by.

Within guidance it is recommended that you should consider carrying out weekly legionella sampling until temperatures are back within range, however there are other options depending on your situation.

How is a system disinfection carried out?

A system clean is carried out across the entire water system, as opposed to just at a tank or one particular outlet. It can be done in two different ways, either a thermal disinfection, which only works on the hot water system, or chemical disinfection.

In thermal disinfections the water heaters are set to operate at a very high temperature, sufficient to kill legionella bacteria, and then all the hot water taps are opened slightly to draw hot water through the entire system.

In chemical disinfections a disinfectant, often chlorine dioxide, is introduced to the water system, the taps are then opened until the disinfectant has been run through to every outlet. The taps are then closed, and the water with the disinfectant in is left to sit in the pipework for a while, to let the chemical get to work killing any bacteria.

After enough time has passed, a neutralising agent is added, and the taps are opened again to purge the disinfectant.

How often should water systems be disinfected?

None of the official guidance documents recommend carrying out regular disinfections of water systems, though you may decide to do this as part of your individual monitoring on a biennial basis – to ensure maximum and continued water safety.

There are several situations however, where a one-off full system disinfection is recommended, these include:

  • Out of specification microbiological sample results

  • If there is a case of legionellosis associated with the water system

  • If the water system has been unused for an extended period and has not been flushed. (Two to three weeks is a good rule of thumb).

  • The installation of a new water system or new components, or significant refurbishment or maintenance of current systems.

  • If tank inspections show significant contamination or stagnation

  • When recommended by your legionella risk assessment

What impact will a system disinfection have on the business?

The impact of a disinfection will vary depending what type of disinfection is carried out. Thermal disinfections are a relatively easy process, it only requires that taps be left to run for five minutes. Chemical disinfections can be much more disruptive, as the outlets cannot be used while the disinfection is carried out, this will be for at least one hour, but may be longer.

TIP - If possible, it is best to carry out chemical disinfections at times when your water system is unlikely to be used, such as early mornings, in the evening or at the weekend in order to minimise disruption to the workforce and business productivity.

Who should carry out a system disinfection?

As with all water treatment tasks, the person carrying out the disinfection should be competent and suitably trained for the task.

One easy way to help work out if the contractor you are using is competent is to see if their company is a member of the LCA (Legionella Control Association) as they conduct audits of procedures and training that their members provide their staff.

You can also directly ask the contractor to provide evidence of competence for their staff members.

Once a disinfection has been carried out, a certificate of disinfection should be provided, this will include information such as when the disinfection was carried out, and the concentration of disinfectant used.

How long should records be kept?

If your company has five or more employees, all records must be stored and accessible. The records kept should include any groups or individual employees identified at being particularly at risk (the elderly, weak or those that suffer from respiratory conditions) and any controls put in place to prevent or control risks.

For companies with less than five employees there is no legal duty to document anything, but it may be useful to keep a written record of assessments and monitoring that has taken place and when.

Records should include the following:

  1. Details of the nominated personnel responsible for conducting the risk assessments, managing the works and implement any written control schemes.

  2. All significant findings from risk assessments or sampling regimes

  3. The monitoring process and execution

  4. Details of the water system(s) and its uses

  5. Whether a particular water system is in or out of use

  6. All results of any monitoring, sampling or risk assessments conducted with personnel names and dates.

Record storing

All the records named above should be stored throughout the period they are current and for at least two years afterwards. Records of any monitoring inspections, sampling or assessments should be retained for five years along with any key dates of the activity.

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