In the second of her articles on facilities management and health and safety, Bridget Leathley offers an overview of preventing legionella in water systems.

During a recent training course with health and safety managers, I was surprised how few could correctly interpret tap water temperatures taken as part of a Legionella management plan. True, it is probably not part of their day job, with technicians or other staff responsible for water management tasks. But understanding the basics puts you in a better position to support your facilities teams with decisions that could impact the health and safety of many, many people.

If you have contractors carrying out water management tasks, you haven’t transferred your legal risk. Your organisation remains responsible for the safety of the water system. When Sentinel Health Care Ltd was prosecuted in 2020 for the death of a patient from Legionnaires’ disease, they pointed towards the role of non-employees, explaining “we were let down by our advisors and contractors and this contributed to the events which led up to this tragic accident.” But in accepting the financial and reputational penalties, they had to admit “the ultimate responsibility remained with us.” They were fined £150,000 with £17,500 in costs, and there was an undisclosed civil settlement to the patient’s family.

Sentinel Healthcare was prosecuted under legislation specific to the healthcare sector (The Health and Social Care Act 2008 (Regulated Activities) Regulations 2014), but most organisations are prosecuted under equivalent requirements in the Health and Safety at Work Act (HSWA) with the potential for heavy fines for organisations and jail time for individuals. In 2019 two managers were given suspended prison sentences for exposing people to Legionella from a cooling tower.

At the extreme, negligence in managing water safety could lead to a corporate manslaughter charge for an organisation, or gross negligence manslaughter for an individual. A manslaughter prosecution was attempted for the council architect complicit in an outbreak of Legionnaires’ disease in Barrow in Furness in 2002. While the manslaughter case fell, the council employee was fined under HSWA.

The Approved Code of Practice for the control of legionella bacteria in water systems (L8) lists other relevant regulations, including the Control of Substances Hazardous to Health Regulations (COSHH) and the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR).

What is Legionella?

If you have a pond, or even a puddle of water after the rain, it is likely to contain Legionella bacteria at a very low concentration. The puddle is unlikely to harm anyone.

However, if Legionella bacteria enter your water system and find favourable conditions, they will multiply. Normally, drinking water containing the bacteria won’t harm you, but they become dangerous if inhaled in an aerosol. Typically, this occurs in showers, but an aerosol can also be created when a toilet is flushed, or when a tap is turned fully on and water splashes from the sink. A fountain in a garden or a jacuzzi will also create an aerosol. The nature of some cooling systems is that they remove excess heat by evaporating water, and this is another way in which an aerosol can be created.

If someone inhales the Legionella bacteria, they can become ill with Legionellosis. Two milder forms of the illness are Pontiac fever and Lochgoilhead fever, which have flu-like symptoms including fever, headaches and muscle aches. More well-known is the extreme version of the illness, called Legionnaires’ disease, which includes a severe and often fatal form of pneumonia.

Legionella bacteria in your water system will grow where they find the ideal temperature, food to sustain them, and are undisturbed for long enough.
Below 20°C bacteria growth is insignificant, although they remain dormant. Between 20°C and 32°C growth accelerates. It is fastest between 32°C and 42°C (human body temperature is around 37°C). Growth starts to slow down from 42°C to 45°C, but doesn’t stop significantly until temperatures are over 50°C. At temperatures above 70°C bacteria are killed almost instantly.

Food for Legionella bacteria can come from insects or other pests getting into your water system, as well as algae, dust, sludge, scale, biofilms and other bacteria. The water system itself can provide food, for example rust in metal pipes and some rubbers or plastics.

Once the bacteria have warmth and food they like to be left alone for a while to grow. Stagnant water allows the bacteria to grow without being disturbed.

How do you stop it?

When we understand what bacteria need to grow, we know how to defeat them. First, stop Legionella getting into your water system. If there is a water storage tank in a loft, check the roof is in good condition, and tank lids are tightly fitted. Second, stop it growing.

Keep the cold water too cold (below 20°C) and the hot water too hot for it. The Health and Safety Executive (HSE) recommends storing hot water at 60 °C or above, so that it reaches a temperature of at least 50°C (55°C in healthcare premises) at the tap. This gives a safety margin to avoid water temperatures below 45°C. As there will be some water in the pipe when you test the temperature you can run the hot tap for one minute, and the cold tap for two minutes before the temperature is read. Insulation of tanks and pipes will help to reduce temperature variation.

Starve the bacteria. An effective cleaning regime is essential. Keep taps and sinks clean and descale or replace shower heads regularly. Maintain pipework and tanks and arrange repairs rapidly when needed. Where there are overflow and vent pipes, screens should be maintained to prevent insects and pests entering the system and providing a banquet for the bacteria. Regular inspections will identify sludge, scale and other nutrients and will prompt action to destroy the food source. This might involve the use of biocides (for which you need specialist advice) or pasteurisation (where water can be temporarily heated above 60°C). Other water treatment options include ultraviolet (UV) irradiation and more experimentally, ultrasound. Monitor the effectiveness of these measures closely.

Don’t let the bacteria sit still. The design of your water system should avoid any deadlegs or pipework that doesn’t regularly have water flowing through it. Where you can’t avoid infrequently used pipework, for example where an emergency shower is part of your safety response, or where a sink is rarely used but is needed occasionally, a flushing regime is needed. The HSE recommends at least once a week, with the frequency determined by assessing the risk.

The final line of defence is to prevent inhalation. Don’t forget the risk to the workers carrying out water management tasks. When they flush an infrequently used shower, tap or toilet they might create and inhale an aerosol containing the bacteria they are protecting other people from. Water management tasks should be risk assessed, with effective controls defined, such as flushing a shower into a bucket of water to avoid spray, and making sure lids are down on toilets when flushed.

Design

Water management should start at design. The inquest into the death of the patient mentioned at the start of this article raised a ‘Report to prevent future deaths’ to the Care and Quality Commission (responsible for overseeing patient safety in care homes) and to RIBA, the Royal Institute of British Architects.

The coroner pointed out: “‘The care home had been constructed with little attention to water safety. There were long runs of pipes and with hot and cold-water pipes set in close parallel proximity, creating a potential for heat exchange.”

This is a clear reminder to ask questions during building or refurbishment projects about whether water safety, and the prevention of Legionnaires’ disease, has been considered in the design. Don’t assume your architect or designer will have considered it.

Useful links

For detailed (free) advice see:

• L8 (HSE, 2013) Legionnaires' disease. The control of Legionella bacteria in water systems. Approved Code of Practice and guidance.
• HSG 274 (HSE, 2024) Legionnaires' disease: Technical guidance. Part 2: The control of Legionella bacteria in hot and cold water systems. This part is relevant to every organisation. Other parts cover evaporative cooling systems (Part 1) and ‘other risk systems’ such as emergency showers, misting systems and vehicle washers (Part 3).
• INDG 458 (HSE, 2012) Legionnaires' disease. A brief guide for dutyholders
• HSE website Legionnaires’ pages at: www.hse.gov.uk/legionnaires

With a first degree in computer science and psychology, Bridget Leathley started her working life in human factors, initially in IT and later in high-hazard industries. After completing an MSc in Occupational Health and Safety Management, she moved full-time into occupational health and safety consultancy, training and writing.