Clean drinking water is a basic prerequisite for health. In Germany, tap water generally leaves the waterworks in very good quality. However, this does not automatically mean that the water at the domestic tap remains hygienic indefinitely. A crucial reason for this is biofilms, which can form unnoticed within the household installation.
What exactly are biofilms?
Biofilms form when microorganisms attach to surfaces. In water pipes, fittings, or hoses, they form a thin, slimy layer that adheres firmly to the inner wall. This structure protects the microorganisms from external influences and allows them to survive for long periods. Crucially, biofilms do not float freely in the water but are attached to surfaces – and therefore often remain undetected in normal water analyses.
How do biofilms form in the household?
Conditions within buildings favor biofilm formation. Water often remains in pipes for hours or days, for example overnight or in rarely used outlets. Low flow rates and lukewarm temperatures also create a favorable environment. Materials such as plastics, seals, or flexible hoses can also play a role, as they provide surfaces to which biofilms can particularly easily adhere.
Why limit values don't capture everything
Drinking water limit values refer to the water itself, not to the inner surfaces of the installation. However, biofilms can continuously release metabolic products or microbial components into the water, without this being immediately measurable. The contamination does not occur acutely, but gradually – through continuous low-dose exposure over long periods.
What does this mean for everyday life?
Biofilms do not necessarily visibly alter the water. Taste, smell, or clarity may remain unremarkable, even though the water's composition changes in detail. Water quality is therefore not static but depends on how the water is used, distributed, and stored in the building.
Why filtration alone doesn't automatically protect
Water filters are often understood as a solution, but they can themselves become part of the system in which biofilms form. Every additional surface in the water circuit can be colonized if maintenance, material selection, and use do not align. Therefore, the crucial factor is not the individual component, but the interaction of all components.
Drinking water doesn't stop at the water meter.
It changes on its way to the tap.
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