WATER QUALITY


Adhesion of water germs on the surface.


Figure 2: Biofilm formation under stagnation as an invisible risk in drinking water systems.


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Adhesion and mucus formation.


2.


Biofilm maturation.


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Balance between biofilm formation and detachment.


Stagnation + biofilm = invisible risk for drinking water hygiene In practical terms, this means that a water system affected


by stagnation is no longer behaving only as engineered pipework. It has become, in part, a biological habitat. That distinction matters in healthcare. Opportunistic


pathogens such as Legionella pneumophila and Pseudomonas aeruginosa do not require dramatic system failures. They depend on favourable conditions: time, suitable temperatures, and the presence of stable microbial communities. Stagnation can help provide those conditions. Just as important, biofilms do not remain static. They can


Figure 3: Circulation loop diagram: an alternative to flushing is the installation of looped pipe systems, which can help prevent stagnation, provided that thermal separation between cold and hot water is maintained. Automated flushing units can also be installed at the end of the pipework as an optional measure.


intermittently release microorganisms back into the water – often unpredictably. This makes them difficult to detect and even harder to control. A sample taken at a single point in time may appear reassuring, while the underlying reservoir persists within the system. In this sense, stagnation does not create biofilms, but it creates the conditions in which they become more established, more resilient, and more difficult to manage.


Why healthcare estates are particularly vulnerable If stagnation were solely the result of poor design, the answer would be comparatively straightforward. Remove the dead legs, correct the oversizing, improve flow, and the problem would largely be solved. But stagnation in healthcare is not only a design issue. It is operational, organisational, and structural.


Hospitals are dynamic places. Wards open and close.


Service lines shift. Departments expand, contract, merge, and move. A basin that is heavily used one year may be largely redundant the next. A room designed for one type of patient pathway may end up serving another. Even where the original design is sound, the actual use of the building changes over time, often significantly. There are also practical realities that estates and infection prevention teams know all too well: temporary decants, delayed openings, phased refurbishments, seasonal pressure, and the need to preserve flexibility in the estate. Every one of these can leave parts of the water system under-used. This is not a niche issue. It is normal healthcare


operation.


Stronger focus on prevention UK guidance has long recognised that safe water depends on both design and operation. HTM 04-01 and HSG274 Part 2 set out the core principles for maintaining hot and cold water hygiene in healthcare and other complex premises. Their emphasis on temperature control, circulation, maintenance, and regular use reflects a long- standing understanding that microbiological risk is shaped by conditions within the system, not merely by end-point testing. What has become clearer in recent years, however, is


that the bar is rising, especially where high-risk patients are concerned. The NHS Estates Technical Bulletin (NETB) No.2024/3


Portable Water Hot (PWH)


sharpened that focus. Issued in the wake of serious concern about waterborne infection risk in specialised clinical environments, it places notable emphasis on design and operation that avoid stagnation, minimise splashing, reduce exposure to drains, and ensure that water systems serving vulnerable patients do not create avoidable opportunities for contamination. It is not only a technical supplement. It is, in effect, a reminder that safe water infrastructure must be thought through as part of patient safety, not just building compliance. That shift in tone matters. It moves the conversation


beyond ‘Have we sampled?’ or ‘Have we documented flushing?’ and towards a more searching question: are we actively preventing the conditions in which harmful microorganisms can establish, persist, and reach patients?


Portable Water Cold (PWC)


The operational burden of flushing Flushing remains one of the most familiar and widely applied control measures, and for good reason. The principle is simple: replace stagnant water with fresh water, restore the intended thermal and hydraulic conditions, and reduce the opportunity for microbial growth.


42 Health Estate Journal August 2026


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