Drinking water in households is often not used for extended periods – for example, overnight, during work, or when no one is home. These phases are referred to as stagnation: the water remains stationary in the pipes and is in direct contact with the installed materials. However, these seemingly uncritical periods have a measurable impact on water quality.
In contrast to flowing water, which is continuously renewed, stagnant water undergoes physical, chemical, and microbiological changes.
Chemical Changes Due to Stagnation
During stagnation, so-called material migration can occur. Substances from pipes, fittings, or seals can be released into the water. Particularly relevant are metals such as lead, copper, or nickel, which can dissolve depending on the material and condition of the installation.
The concentration of these substances increases with the duration of stagnation, as no exchange with fresh water takes place. This means that water that has been in the pipes for a long time can have a different chemical composition than water directly from the main supply.
Impact on Microbiological Processes
In addition to chemical effects, stagnation also promotes microbiological changes. In still water, microorganisms can multiply more easily and form so-called biofilms on the inner surfaces of the pipes.
These biofilms consist of complex communities of bacteria and other microorganisms. They can release metabolic products that affect both the sensory perception and the hygienic quality of the water.
Even if the water at the supply network meets the requirements, its quality within the house installation can change due to such processes.
Temperature as an Additional Influencing Factor
Temperature amplifies many of these effects. Stagnant water quickly reaches ambient temperature, especially in warm months or in pipes in unheated areas.
Higher temperatures promote both the solubility of certain substances and the activity of microorganisms. This can accelerate both chemical and microbiological changes.
Why Stagnation Is Often Underestimated
Stagnation periods are unavoidable in daily life but are rarely consciously considered. The quality of drinking water is often assessed exclusively at the source, but not at the actual point of tap in the household.
A significant part of the changes only occurs within the house installation – especially during phases without water flow.
Conclusion
Stagnation is a central but often underestimated influencing factor on household water quality. Due to the lack of exchange with fresh water, both chemical and microbiological changes can develop, affecting the composition and perception of the water.
A holistic view of drinking water quality must therefore consider not only the initial quality but also the conditions within the house installation.
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