Drinking water is chemically active. Once it enters household plumbing, it interacts with the materials it contacts. Plastics, elastomers, seals, and flexible hoses can release trace substances into the water through a process known as material migration. This mechanism is a well-established contributor to water composition at the point of use.
Material migration arises because polymer-based materials contain additives such as plasticizers, stabilizers, and processing aids. Over time, and depending on temperature and contact duration, these compounds can diffuse into the surrounding water. Studies demonstrate that migration rates are highest during initial use and after prolonged stagnation, when water remains in contact with materials for extended periods [German Environment Agency, Assessment of materials in contact with drinking water, https://www.umweltbundesamt.de/publikationen/bewertung-von-materialien-im-trinkwasserkontakt].
Operating conditions strongly influence migration intensity. Higher temperatures accelerate diffusion processes, making warm water systems and mixing valves particularly relevant. Flexible hoses and soft elastomer seals often show higher migration potential due to their larger effective surface area and material composition [World Health Organization, Guidelines for drinking-water quality – materials, https://www.who.int/publications/i/item/WHO-FWC-WSH-17.05].
Regulatory frameworks address material migration through standardized testing and approval schemes. These assessments define acceptable release levels under controlled conditions. However, they represent averaged scenarios. Real households vary widely in usage patterns, stagnation times, and temperature profiles, which can lead to exposure situations that differ from test assumptions [European Commission, Drinking Water Directive (EU) 2020/2184, https://eur-lex.europa.eu/eli/dir/2020/2184/oj].
From a health perspective, the key issue is not acute toxicity but long-term low-level exposure. Research on overall exposure pathways indicates that drinking water can contribute measurably to the intake of certain plastic-related substances, especially when combined with other environmental sources [European Food Safety Authority, Plastics and food contact materials, https://www.efsa.europa.eu/en/topics/topic/plastics].
This does not imply that tap water is unsafe. It highlights that water quality is shaped not only by treatment and distribution, but also by the materials within the home. Contact time, temperature, and material choice all influence what ends up in the glass.
Drinking water does not stop evolving at the treatment plant.
It continues to change inside the home.
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