Summer is the peak season for legionella growth, with incidents of Legionnaires’ Disease typically spiking between July and October However, while summer is a good reminder to be vigilant about legionella management and water hygiene, the risks are present throughout the year. In March 2026, for example, the UK Health Security Agency (UKHSA) identified eight cases connected to north west or south west London, with a further 13 cases under investigation.
Bathrooms are one of the most important areas to consider during the year, because they combine several legionella risk factors such as stored water, warm temperatures, infrequently used outlets and aerosol-producing fittings. A well-designed bathroom should be aesthetically pleasing while also supporting good water hygiene.
LEGIONELLA RISK FACTORS
While outbreaks are often associated with large-scale systems such leisure facilities, everyday water outlets also need careful consideration. The Health & Safety
Executive (HSE) identifies hot and cold water systems, spa pools and cooling systems as examples of purpose-built systems where Legionella outbreaks can occur. Risk increases where systems:
• Operate within the Legionella growth range (approximately 20-45°C)
• Create aerosols (showers, spray taps, spa jets)
• Store or recirculate water.
MINIMISE DEAD LEGS
Sections of pipework where water can remain unused for extended periods are a well-known risk factor. For example, a bathroom designed with an additional shower connection for future expansion may create a section of pipework where water becomes stagnant. Where future-proofing is required, designers should consider how these connections will be managed until they are brought into regular use.
SELECT ACCESSIBLE OUTLETS
Taps, shower heads and spray fittings should be accessible for routine cleaning, descaling and replacement. Components that are difficult to remove or maintain can discourage effective maintenance and increase long-term risk.
USE TMVS
Thermostatic mixing valves (TMVs) are commonly specified to deliver safe outlet temperatures in settings like hospitals, schools and public facilities. By mixing hot and cold water near the outlet, they help to prevent scalding during handwashing while allowing hot water storage at temperatures which inhibit bacteria growth, around 60°C.
WATER STORAGE AND TANKS
Where stored water forms part of the system, tanks should be appropriately sized, insulated, covered and accessible for inspection and cleaning. Oversized tanks or poorly maintained storage can create conditions that encourage bacterial growth.
PIPEWORK ACCESSIBILITY
Concealed services may improve aesthetics, but pipework should still be accessible for inspection, temperature monitoring and remedial work. If maintenance teams cannot reach critical components, compliance becomes difficult to demonstrate.
During construction, pipework may be installed months before a building is occupied. If water remains stagnant within the system due to construction delays, phased commissioning or reduced water usage, conditions can become favourable for bacterial growth, particularly during the warmer months.
COMPLIANCE AFTER HANDOVER
Even the best-designed system requires ongoing management. Under the Health and Safety Executive’s Approved Code of Practice (ACoP L8), duty holders are expected to assess the risk of Legionella and implement suitable control measures for hot and cold water systems. An effective regime may include:
• Routine temperature monitoring
• Water sampling where appropriate
• Annual inspection of storage tanks and calorifiers, or more frequently depending on risk
• Weekly flushing of infrequently used outlets
• Cleaning and descaling of shower heads and taps
• Servicing of TMVs at least every 12 months.
Finally, accurate record keeping is absolutely critical. In the event of an inspection, it must be possible to demonstrate that monitoring and maintenance have been carried out in accordance with the agreed control regime.
Most people use bathrooms everyday without considering any risk, taking clean and safe water for granted. Designers and specifiers have a duty to build legionella prevention into healthy and resilient buildings from the outset, rather than treating it as a maintenance issue following completion.
The summer months are a useful reminder to review water hygiene measures, but effective Legionella control must be embedded throughout the entire lifecycle of a building, from design and installation through to ongoing operation and maintenance to ensure year-long compliance and safety.
www.swiftclean.co.uk