WATER SAFETY
matter might react, impact and result in the formation of disinfectant byproducts that will result in a health risk to patients.
Microorganisms tolerant to biocide exposure Equally important is the recognition of how the use of a biocide will select for tolerant organisms, particularly at the concentrations permitted in drinking water systems.14-18 Microorganisms which are tolerant to biocide exposure include waterborne pathogens and populations protected within biofilms or hosts such as protozoa. Whilst much merit is placed on the oxidative action of biocides to penetrate biofilms and enable sloughing, the impact is limited compared to the extent of biofilm formed, and if the operating conditions remain conducive for biofilm formation there is little evidence to suggest that continued use of biocide will prevent biofilm formation. Many studies have reported that there are important caveats in the application of biocides in a drinking water network and prior understanding of a system’s water chemistry along with the operating parameters are critical to determine its effectiveness.19-22
Biocides may select for tolerant organisms which may predispose them to being antibiotic resistance.23-29
Efforts
must be made to prevent the selection of antibiotic- resistant strains as healthcare facilities are unable to combat the rise of such infections due to the contamination risks within their built environment from the water and wastewater interfaces. Other control methods do not appear to result in such selective pressures, including UV irradiation, filtration (including point of use filters), physical removal of contaminated componentry and underused outlets which should be preferentially assessed. Whilst the US, China, Italy and UK have a significant water treatment industry built around the provision of biocides into healthcare and other markets, many other countries either restrict or prohibit the use of secondary systemic biocide within drinking water systems. Central European countries, such as Germany, have guidance and legislation in place which bans continuous biocidal treatment (both primary and secondary use) unless there is a specific argument behind the need for
such treatment.30 Such strategies focus on mandatory
compliance with a Code of Practice for water suppliers as well as Dutyholders, and have a strong requirement towards water system design, operation, maintenance and the materials in contact with water. Water suppliers are obliged to provide water to the public water system that does not pose any risk to human health in the absence of disinfectants.30,31 Temperatures between 55 °C and 60 °C in all buildings and cold-water temperatures less than 25 °C must be achieved within 30 seconds at each outlet. Approved materials in contact with water are listed by the Federal Environmental Agency which specifies certifications and installation of devices that are tested for use. In addition, there are mandatory legal requirements for use of outlets within a 72 hour period, annual sampling within public buildings for Legionella and at least every three years for commercially used buildings.30,32-34 German law lists threshold values for chemical substances and physical parameters, and Dutyholders have to provide test results from DIN ISO 17025 accredited laboratories.30 Accordingly, if a water system is designed, maintained and operated according to the Code of Practice, microorganisms should be controlled (< 100 CFU/100ml Legionella spp.) and Legionella concentrations not exceeded during regular mandatory sampling.30,35 The German Drinking Water Ordinance allows
Dutyholders to provide drinking water to consumers only when their water systems ‘at least comply with the Code of Practice’. Any deviations from the Code of Practice must be immediately identified and eliminated.30
Successful
remediation will be confirmed by extended sampling after three, six and nine months post-remediation.32
Secondary
disinfection measures cannot compensate for design or operation engineering defects, nor offer protection to users. Compliance with the legal requirements is monitored
by the Health Authorities: any exceedance of the technical specifications are communicated directly to the Health Authorities by accredited laboratories.30
Dutyholders must
immediately complete a Risk Assessment and implement the recommended engineering control measures.
Dr Jimmy Walker
Dr Jimmy Walker is a water microbiology expert with over 30 years experience. He previously worked for Public Health England where he worked on biofilms, Legionella spp., Pseudomonas aeruginosa and Mycobacteria spp. He also worked with the Department of Health (DH England) and the Health and Safety Executive in writing guidance on water microbiology in healthcare. He contributed to the NETB Guidance on non-nontuberculous mycobacteria (NTM) and other waterborne pathogens. Jimmy is the former Chair of the Central Sterilising Club and has published a practical guide to enable healthcare workers to manage waterborne hazards.
January 2026 Health Estate Journal 37
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