WATER SAFETY
are post-flush counts in specific hot spot locations within the building, this will likely indicate a peripheral contamination (investigate components close to the outlet) or a local dead leg, neither of which will be addressed by systemic biocide application.
n Concentration – consistent and sufficient biocide concentrations throughout the water system are required as low concentrations will result in microbial growth.
n Contact time – insufficient contact time will not impact any free-living microorganisms.
n pH value – biocides may have an optimum pH range within which they will be effective, therefore understanding how acidic or alkaline your source water is necessary.
n Temperature – biocides may have an optimum temperature range within which they are effective, and “gassing off” effects may be expected in hot water systems.
n Organic matter – a high concentration of particulate matters, unseen by the human eye, will result in degradation of the biocide concentration as it reacts with organic particulate matter as opposed to microorganisms or biofilms. A silt density index test should be completed to identify the general level of loading, and scanning electron microscopy and energy dispersive spectroscopy can detail the materials present.
n Microbial concentration – high number of microorganisms will degrade the biocide concentration.
n Biofilms – to be effective biocide a must penetrate the biofilm. Some oxidising biocides will impact the surfaces of biofilm, although penetration of thick sticky matrices is usually limited and microorganisms remain viable.
n Stagnant water – hydraulic balance must ensure circulation of hot water, no dead legs or blind ends, and water outlets or plumbed in equipment need to be used or flushed on a regular basis (daily, ideally multi- daily) to maintain appropriate biocide concentration through the periphery of the pipework.
Figure 1: Steady state operation: flow diagram illustrating steady state operation with biocide use in a water system.
Health authorities can request the Risk Assessment and verification results of remedial measures at any time.30
The
Health Authorities are also directly involved in outbreaks, particularly within healthcare buildings.
When to implement a systemic biocide strategy Where there is difficulty in maintaining consistent temperature control in healthcare water systems or a loss of microbial control, it may be prudent to use systemic biocides (Figure 1). There are a number of biocides that could be considered including chlorine, chlorine dioxide, monochloramine, hydrogen peroxide and silver-copper ionisation as secondary control strategies. However, the effectiveness of biocides is impacted by a number of parameters, including: n Systemic contamination – if high post-flush microbiological results from outlets spread across a wide location range are present, this will likely indicate systemic contamination. However, if corresponding pre-flush microbiological results are higher, or there
38 Health Estate Journal January 2026
Biocides will have undergone laboratory tests under controlled and reproducible conditions to demonstrate performance, including effectiveness against waterborne pathogens and biofilms under short and long-term contact times. However, there is a difference between the laboratory setting and a healthcare in-premise water system. Similarly, there is a difference between laboratory grown microorganisms versus professional waterborne pathogens recovered from operational water systems. Whilst laboratory validation data is helpful, it should not be the only reference point when considering performance under real-life conditions. Biocides present a risk when used in healthcare water
systems. For example, controls must be in place to prevent chemicals from passing into renal and haemodialysis units as the presence of chemicals in the water provided to these units will lead to fatalities. In addition, biocides result in corrosion and shorten the life span of installed components. As such, biocides should be chosen with care, must comply with the appropriate water regulations and their application must be fully risk assessed.
Summary Water systems are immensely complex, and microorganisms take advantage of that complexity by multiplying and finding niche environments in which to hide and grow. Whilst temperature is the primary method of control, required temperatures can often be difficult to achieve due to poor design, inadequate construction
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