Congratulations to the Royal Society for Public Health who organised an insightful lunchtime webinar on 3rd September 2025 (https://www.rsph.org.uk/events/) delivered by Professor Michael Gormley from Heriot-Watt University, Edinburgh and chaired by Dr Susanne Surman-Lee (lead author of NETB 2024/3). The topic was “Managing the Risk from Drains and Wastewater in Healthcare Premises.” It is clear that the building drainage system, so often overlooked on the hospital risk register, is alive with turbulence, complex fluid mechanics coupled with air movements leading to the generation of air pressure transients. These air pressure transients cause the wastewater interface in the UBend to be disturbed (mostly invisibly), generating aerosols which Prof Gormley has evidenced to spread organisms from the drain into the handwash basin, tap outlet and beyond. Concerns regarding the spread of pathogens, and in particular antimicrobial resistant ones, makes water outlets, drains and splash zones surrounding any handwash basin, sink, shower, toilet etc., of critical importance and reflects highest risk when installed in patient care areas.
Professor Gormley discussed the inter-connectivity of drainage systems, a huge network within hospitals, all connected to the main sewer. Focus is typically on the risk from leakage, blockage or slow flow and the impact that has on patients, equipment and surfaces. However, this talk confirmed that it is the air within wastewater systems that offers the greater and “unseen” continuous risk to patients in proximity to water services. The movement of air within the normal operation of the wastewater drainage system creates turbulence, which in turn creates aerosols. Work was presented from a full scale pilot drainage system, covering 129 meters high, where “real life” testing of pressure transients could be evidenced through the use of settle plates in and around the handwash basin. This data has recently been published in the Journal of Hospital Infection and should be shared at Water Safety Group Meetings.
What should Hospital Water Safety Groups do? Firstly, to look at hospital drainage systems in a different way – recognise their delicate balance of pressure differentials and air flow. Ensure that “Wastewater” is included on the agenda for all Water Safety Group meetings – as a minimum ensure drainage schematics are up to date and that reports of blockage and slow flow are regularly discussed with investigation, remediation and verification pathways followed to mitigate problems encountered. We must all recognise the air within wastewater drainage systems as the hazard and the unseen risk from release of contaminated aerosols from the drain interface at all water services. Understand if there are improvements that can be made to reduce pressure waves within wastewater systems. Take extreme care when disturbing the system – for example when dealing with blockages – as this will cause waves of pressure differentials in other areas of the wastewater network. Whilst there are developments such as water-less traps, vacuum toilets, use of splash screens etc, the best practice is to minimise the presence of water in patient care areas and adopt processes which reduce risk to the patient
Gormley’s research makes the recent data and actions taken at Guys & St Thomas’ Hospital doubly important. Snell et al have reported on the use of continuous remote sensor monitoring of the hot and cold water supply to all hand wash basins in one of their Intensive Care Units which had a known waterborne pathogen problem. This data clearly identified 2/15 wash hand basins which were underused (i.e. not used daily on multiple occasions). It was also noted that with space restrictions on the ward that patient beds or other critical surfaces were positioned within splash zones. The two least used outlets, identified with the remote sensor monitors, were removed, without any negative impact on hand hygiene compliance. Not only have this team removed the stagnancy risk from underuse of the hot and cold water supply, but they have also removed the source of exposure to contaminated wastewater aerosols in these two areas.
Hospital design teams for new build and refurbishment must consider human ergonomics for using handwash basins – just because it is there does not mean that it will be used – and face the reality of the risk it can bring to vulnerable patients. Adopting a proactive risk assessment approach to the installation of hospital water services – as per the latest guidance within NHS Estates NETB 2024/3 – ensures occupant and patient safety can be recognised as the priority with a reduction in risk from waterborne pathogens.
If you would like to discuss hospital wastewater systems and the risk from air movements and aerosolisation, or using continuous remote monitoring of hot and cold water systems, or reducing the presence of water services in high risk patient environments, please contact us
References
Gormley M, Kelly DA, Campbell DP, Aspray TJ, Dight T. The role of air pressure transients on the spread of bacteria from wash-hand basin sink traps in hospital en-suite bathrooms: A laboratory-based pilot study. J Hosp Infect. 2025 Aug 12:S0195-6701(25)00242-7. doi: 10.1016/j.jhin.2025.07.026. Epub ahead of print. PMID: 40812395.
Snell LB, Hussein A, Abadioru O, Dibbens M, Whitehorn J, Nichols R, May L, Coates S, Barrett NA, Winteridge H, Otter JA, Goldenberg SD. Use of continuous remote sensor water temperature monitoring to rationalise provision of clinical hand wash basins in an ICU with water safety issues. J Hosp Infect. 2025 Aug 11:S0195-6701(25)00237-3. doi: 10.1016/j.jhin.2025.07.021. Epub ahead of print. PMID: 40803379.