WATER QUALITY
When water stands still: the invisible risks
A water system affected by stagnation risks transforming into a rich biological habitat for opportunistic pathogens. Here, Holger Eggert, head of product management and business development at Aqua free Group, looks in depth at why stagnation remains one of healthcare’s most underestimated risks and what estates teams need to do in order to prevent it.
In healthcare estates, risk does not always arrive with a siren. More often, it develops quietly, within systems that appear to be functioning normally while gradually drifting away from the conditions they were designed to maintain. Few issues illustrate this better than stagnation in potable water systems. Water, in a healthcare setting, is almost instinctively associated with cleanliness and safety. It is the medium of hand hygiene, patient washing, clinical cleaning, food preparation, and countless routine activities that support care. Yet that sense of safety is tied to a basic assumption: that water is moving, turning over, and remaining within the parameters intended by design and operation. In reality, it often is not. Across modern healthcare estates, water regularly sits
idle. Taps are used less often than expected. Clinical areas are refurbished, decanted, or repurposed. Rooms may stand empty for days, sometimes weeks. Some outlets are installed for flexibility, only to become rarely used in practice. In those moments, the system does not simply pause. It changes. And those changes are rarely benign. Stagnation is not an unusual event. It is a routine feature of complex buildings. That is precisely what makes it dangerous. It does not arise only from failure. It emerges from ordinary operational realities: changing occupancy, intermittent use, legacy infrastructure, over-capacity, and the unavoidable mismatch between how systems were planned and how buildings are actually used. Despite this, stagnation is still too often treated as a secondary concern, something to be managed through occasional flushing, rather than recognised as something that can materially increase risk in healthcare water systems.
What happens when water stops moving
One reason stagnation remains underestimated is that it is often imagined as a problem of prolonged neglect. The phrase itself can suggest water left untouched for weeks. In practice, the process begins much earlier. Once flow is reduced or absent, the conditions
within the system begin to shift. Water age increases, temperatures begin to drift, and the hydraulic forces that normally act on internal surfaces are reduced. These changes do not initiate biofilm formation – biofilms are a natural and ubiquitous feature of water systems – but they significantly influence how they develop and persist.
Under conditions of low or no flow, reduced shear allows microorganisms to remain attached more easily, while increased residence time provides greater
Stagnation
opportunity for growth and interaction with surfaces. What may begin as initial adhesion can more readily progress into stable colonisation. This is the point at which biofilms become more consequential.
Biofilm is not simply a coating of bacteria on a pipe wall. It is a structured microbial community embedded in a protective matrix. Once established, it changes the behaviour of the system. It provides protection from environmental fluctuations and physical disturbance, retains nutrients, and enables microorganisms to persist and multiply in ways that free-floating cells cannot.
In a modern healthcare estate, many taps are underused for significant periods.
Figure 1: Stagnation in building water distribution systems.
August 2026 Health Estate Journal 41
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