WATER SAFETY


Legionella control in hospital water systems


Harijeet Singh BSc, Business Development manager and Vikram Bamra Beng, Technical Services manager at Goodwater, present results from a three-month evaluation of monochloramine disinfection across two oncology hospitals within the same NHS Trust, both of which had experienced persistent Legionella pneumophila contamination despite conventional control measures. The study explores the operational and microbiological impact of introducing a controlled monochloramine dosing system to reduce contamination in healthcare water systems.


Waterborne pathogens such as Legionella pneumophila present an ongoing infection risk in water systems within healthcare facilities, particularly those with large and complex plumbing systems. Oncology hospitals are considered especially higher risk, owing to the immunosuppressed nature of their patient population and their dependence on consistent, microbiologically safe water. Traditional Legionella control methods – such as


thermal disinfection, localised disinfection of affected outlets using biocides such as chlorine and hydrogen peroxide, and point-of-use filtration – can offer temporary or partial efficacy but often fail to address entrenched biofilm contamination. Aged infrastructure, temperature fluctuations, and variable water usage patterns can further promote recolonisation, leading to repeated positive samples and high operational burden for estates teams. Monochloramine (NH₂Cl) has recently emerged as


a promising alternative secondary disinfectant within the building services sector in the UK. Its stability, ability to penetrate biofilms, and capacity to maintain residual effectiveness throughout distribution systems make it particularly well-suited to healthcare settings.


Materials and methods The three-month evaluation was conducted by Goodwater at the following oncology hospitals: n London site: 113 beds, seven operating theatres, and 16 critical-care beds.


n Surrey site: 106 beds, two operating theatres, and 16 critical-care beds.


Both hospitals had a long-standing history of L. pneumophila positivity within blended outlets and showers, despite frequent disinfections using silver stabilised hydrogen peroxide (6 hours contact time) and temperature management regimes. In conjunction with the Trust, a monochloramine


generator (Sanikill Lite, manufactured by Sanipur SpA, Italy) was installed by Goodwater at each site within the primarily affected blocks. The generators were situated on a side-stream installation on the mains cold-water service feeding the cold water storage tanks within each block. At both sites, hot water services are generated via plate heat exchangers, fed from these cold-water storage tanks. At the London site, a water softener is also present on the feed to the hot water system. This setup meant that both the hot and cold water systems received monochloramine treatment via the single dosing station. The Sanikill system generates monochloramine in


situ through the controlled combination of pre-cursor chemicals; sodium hypochlorite and ammonium sulphate. The dosing rate was monitored and adjusted to ensure residual concentrations remained at ≤3.0 mg/L at any drinking water outlets, compliant with international drinking water standards. Following the start-up of the Sanikill systems, no other supplementary disinfection, thermal interventions, or additional flushing (over and above what was already in place) was conducted during the trial periods. Any previously undertaken localised disinfections were ceased, meaning there was a complete reliance on traditional flushing and disinfection using monochloramine only. Following initial start-up of the generators at each site, Goodwater’s Sanikill engineers attended site on an initial weekly basis over the first month, to ensure adequate levels of monochloramine were being detected throughout the systems, especially at those points known to have had presence of Legionella bacteria. Residuals were also monitored by the hospitals’ site maintenance teams using a handheld colorimeter test-kit. Monthly inspection and calibration of the Sanikill generators were performed by Goodwater to maintain accuracy and safety. Unlike other commonly used biocides such as chlorine dioxide or hydrogen peroxide


Sanikill Lite installed at hospital in Surrey.


January 2026 Health Estate Journal 55


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