KTW-BWGL

Definition and Purpose of the KTW-BWGL

KTW-BWGL stands for “Bewertungsgrundlage für Kunststoffe und andere organische Materialien im Kontakt mit Trinkwasser” (“Assessment Basis for Plastics and Other Organic Materials in Contact with Drinking Water”). It is published by the German Environment Agency (UBA). The KTW-BWGL is a technical regulation that defines how organic materials are assessed when they come into contact with drinking water.

Its purpose is clearly oriented toward health protection and drinking-water hygiene. The decisive question is: which substances can transfer from a material into drinking water? This substance transfer is called migration (chemical release of constituents). As a result, the KTW-BWGL is intended to ensure that materials are used in such a way that they do not adversely affect the drinking water, because only limited and assessed amounts of substances may enter the water.

Scope: Which Materials and Applications Are Affected?

The KTW-BWGL becomes relevant as soon as organic materials are used in areas serving the extraction, treatment, storage, or distribution of drinking water. In practice, this affects many components in drinking-water installations, because even small parts can have direct contact with the water.

On the material side, this mainly concerns plastics as well as elastic organic materials, which are common in sealing technology. These include elastomers (rubber-elastic materials, for example in O-rings) and thermoplastic elastomers (TPE) (elastic materials that can be processed like thermoplastics). In the KTW-BWGL, such groups are regulated as separate areas, among other things via annexes (e.g., Annex D for elastomers, Annex E for TPE).

Relevance for Seals, Sealing Materials, and Assembly-Near Parts

In sealing technology, the KTW-BWGL is particularly important, because seals are frequently in continuous and large-area contact with drinking water. As a result, the question of whether constituents of the recipe migrate into the water becomes very concrete in practice.

With elastomers and TPE, in principle different substance groups can migrate — for example additives (auxiliary substances used to set properties), processing aids, or residual substances from cross-linking (chemical reaction for curing). Precisely because seals are often used close to the consumer, the assessment of substance release becomes a central criterion for material selection and component approval.

Basic Principle and Typical Test/Assessment Logic

The basic principle of the KTW-BWGL is the control and limitation of chemical substance release into drinking water. What is mainly assessed, therefore, is the chemical/toxicological suitability of a material for drinking-water contact. As a rule, this means that the material is tested and assessed in such a way that its release products can be identified, quantified, and evaluated with respect to health relevance.

A typical element is the use of positive lists. A positive list is a list of permissible starting substances that may be used under defined conditions. In addition, which release products (e.g., reaction or degradation products) and impurities can occur is also considered. In practice, alongside the pure substance amount, the question often plays a role of whether the material affects the water sensorially — that is, changes odor or taste. This sensory side is relevant for operators and users, even though the core of the KTW-BWGL remains the chemical assessment.

Distinction: Chemical Safety vs. Microbial Growth

The KTW-BWGL primarily considers whether a material can be problematic through substance migration. This is a different test concept from the question of whether a material promotes microbial growth. Biofilms can develop even when chemical release is low.

For this reason, microbiological aspects are frequently considered additionally in practice, via separate test concepts and regulations. For sealing technology, this distinction matters because it makes material approval more realistic: a material can be well evaluated chemically, while the operating situation may still make an additional microbiological assessment sensible.

Verification in Practice: Conformity Confirmation and Key Deadlines

So that the requirements do not remain theoretical, a documented verification is needed in practice. Here, the conformity confirmation is often used. This refers to a written confirmation that a product or material meets the relevant drinking-water hygiene requirements. The basis is a UBA recommendation on conformity confirmation, which structures the verification path.

The time frame is also important. The KTW-BWGL has been binding since 21 March 2021. However, for certain material groups, transitional provisions exist that can lead to parallel statuses in projects. For elastomers (Annex D) and TPE (Annex E), binding requirements have been postponed to 1 July 2026. In sealing technology, this is relevant because many drinking-water seals fall into precisely these material groups, and approval and changeover strategies depend on it.

Dates and Terms

When requirements, recipes, and verifications need to be brought together, specialized technical and regulatory consultation is often sensible.