In drinking water installations, there are areas where water is rarely or never used. These include so-called dead legs as well as rarely used tapping points such as guest WCs, outdoor connections, or unused faucets. These areas present special conditions that can affect water quality.
Since they often go unnoticed in everyday life, they are frequently underestimated.
What are dead legs?
Dead legs are pipe sections where no regular water exchange takes place. The water remains there stagnant for longer periods and is continuously in contact with the surrounding materials.
Rarely used tapping points have a similar effect, as water flow only occurs sporadically.
Stagnation as a central factor
In dead legs and rarely used areas, pronounced stagnation occurs. This extended residence time leads to an intensification of physical, chemical, and microbiological processes.
Without regular exchange with fresh water, changes in the water can accumulate and stabilize.
Chemical changes
During stagnation, substances from pipe materials, seals, or fittings can migrate into the water. The concentration of these substances increases with the duration of stagnation, as there is no dilution by incoming water.
This particularly affects areas with unfavorable material combinations or older installations.
Microorganisms and biofilms
Stagnant conditions also promote microbiological processes. Microorganisms can multiply more easily in these areas and form stable biofilms.
These biofilms serve as a reservoir for microorganisms, which can enter the water flow when the system is used again.
Influence on the overall system
Although dead legs are locally limited, their effects can influence the entire system. Due to changes in pressure and flow, particles or microbiological components from these areas can be mobilized and transported to other parts of the installation.
Thus, local stagnation zones also affect more distant tapping points.
Perception in everyday life
Changes caused by dead legs often only become apparent during use – for example, through altered taste, odor, or temporary turbidity after prolonged disuse.
These effects are usually temporary but indicate processes within the installation.
Conclusion
Dead legs and rarely used tapping points represent relevant but often overlooked factors influencing water quality. Due to stagnation, chemical and microbiological changes can develop that originate locally but can affect the entire system.
A comprehensive assessment of drinking water quality should therefore also consider these areas of the building installation.
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