Drinking water quality in focus: Safe to drink, but not free of contaminants

Residues from pharmaceuticals, household chemicals and fertilisers continually enter wastewater and, in turn, our waterways. But how concerning are these trace substances?

Water is a resource that should not be treated carelessly. That is understandable: everyone relies on access to clean drinking water and expects it to be safe. Drinking water treatment is tightly regulated, with strict European limits that must be met. These rules were defined in the EU Drinking Water Directive of 1991 and include guideline values for microbiological, chemical and radiological parameters. Germany implemented the EU directive through its Drinking Water Ordinance.

To meet these limits, plant operators have obligations under water management legislation. This also specifies testing intervals by certified laboratories. In practice, strict requirements and public scrutiny mean that drinking water guideline values are not exceeded.

There are currently no statutory requirements for the adequate removal of trace substances. Why is that? Current studies suggest that the concentrations measured are considered harmless to humans. Nevertheless, the issue remains part of public debate, and overall contamination is increasing. The aim is to filter out these substances as effectively as possible. Residues of X-ray contrast agents are particularly difficult to remove. They can enter the drinking water network through hospital wastewater, for example.

The most extensive initiatives so far are in municipal wastewater treatment. Sewage treatment plants, particularly in Baden-Württemberg and North Rhine-Westphalia, are being upgraded to a fourth treatment stage. Wastewater is currently treated mainly using mechanical, biological and chemical processes, the three treatment stages. Large plants handling substantial volumes of hospital wastewater or urban residues face particular difficulty removing trace substances using only these three stages. New methods such as ozonation or treatment with powdered or granular activated carbon can remove some substances at rates exceeding 90%.

A European comparison shows that Switzerland has taken a more consistent approach, particularly in legislation. A revision of its Water Protection Ordinance legally required the upgrading of 100 wastewater treatment plants by 2035. Across Europe, however, Switzerland is an exception, so unfortunately there is no uniform strategy.