Legionella risk in dental practices WATER TREATMENT, DRAINAGE & PIPED SERVICES


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Dental practices, like all other healthcare premises, have a legal duty to provide safe care and treatment to patients and comply with Health and Safety law, writes Charlie Brain, senior consultant, Water Hygiene Centre


ental practices are typically supplied by the public mains water supply, which is used for handwashing, cleaning, decontamination and drinking. The use of this water


by staff and patients represents a risk of exposure to legionella bacteria, which must be managed.


Dentists and legionella guidance


The Health & Safety Executive’s (HSE) Approved Code of Practice (L8) provides advice on how to comply with legal duties under the Health and Safety at Work etc Act 1974 (HSWA) and the Control of Substances Hazardous to Health Regulations 2002 (COSHH). Healthcare providers, such as dental practices, must also meet the Health and Social Care Act to prevent and control infection risks.


Practical advice on managing water systems and legionella bacteria is found in HSG 274 Parts 1–3. As healthcare premises, dental practices should also follow Department of Health (DoH) documents HTM04-01: Safe Water in Healthcare Premises; and HTM01-05: Decontamination in Primary Care Dental Practices.


Management plans and governance


HTM01-05 states that Registered Managers have a duty of care under the HSWA. They must ensure water supply, storage and distribution comply with best practice guidance — namely HSE’s ACoP L8 and DoH’s HTM 04-01. In practice, dental practices should have:


* A legionella risk assessment * A written scheme of control (operational plans, drawings, procedures and incident plans)


* A legionella training programme


HTM04-01 (2016) also refers to water safety plans, detailed further in BS 8680:2020 Water Safety Plan – Code of Practice.


Legionella risk assessments


Risk assessments are a requirement of the above regulations, supported by ACoP L8 and HSG 274. BS 8580-1:2019 explains what should be considered in method and reporting. Findings must be informed by HTM04-01 and HTM01-05, and should examine:


* The current written scheme of control * Effectiveness of implementation (management, training, plans)


* Water systems (cold water tanks, hot water, fittings, system design and operation) * Dental equipment


The recommendations form the basis of an action plan and updates to the written scheme.


Dental equipment


Dental chairs include a water supply that can be aerosolised and expose patients and staff, so must be assessed. Water is supplied either from the building’s cold water system or self-contained bottles of distilled/reverse osmosis water. Dental unit water lines (DUWLs) use long,


narrow tubing prone to biofilm formation, where bacteria such as legionella and Pseudomonas aeruginosa can grow. This presents a risk when water is aerosolised or contacts wounds. Studies have shown dentists develop higher antibody levels compared to those unexposed. A flushing regime and maintenance reduce biofilm risk. HSG 274 Part 3 and HTM01-05 recommend:


CQC adds further advice: flush DUWLs 2–3 minutes at the start of sessions, 20–30 seconds between patients; isolate mains water with bottled systems; use only distilled/RO water; and never refill bottles with tap water. Confusion exists over whether bottles should


be removed daily, as manufacturer advice varies. With some guidance now a decade old, practices must balance official documents with up-to-date manufacturer instructions.


Microbiological monitoring


Routine microbiological testing of hot and cold-water systems is generally unnecessary, as systems are supplied with drinking-quality water. However, BS8558 recommends testing to check process efficacy or water quality changes. Testing may be required during system commissioning, tank cleaning, or in response to concerns or clinical cases. Legionella sampling within domestic systems is only needed if water is stored, temperatures fall, treatment regimes fail, or if there is a suspected case. For dental equipment, HSG 274 and HTM01-05 say sampling is guided by the risk assessment. CQC advises testing only after problems such as taste or odour issues.


Summary


Dental practices must follow the same regulations as other buildings while also observing healthcare-specific HTMs. In addition to domestic systems, dental chairs and DUWLs create further risk, reinforcing the need for robust legionella risk assessments, written schemes of control and ongoing maintenance to protect patients and staff.


Task


Drain down, clean, flush and disinfect all system components, pipework and bottles.


Clean storage bottles, ensure they are rinsed with distilled water or Reverse Osmosis [RO] water, then drain and leave inverted overnight.


Frequency


Twice daily [typically at the start and end of each working day]. Disinfectant contact times as recommended by the manufacturer.


Daily.


36 BUILDING SERVICES & ENVIRONMENTAL ENGINEER OCTOBER 2025


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