How to ensure a clean taste and odourless drinking water
The taste of water varies from location to location, but it must never be affected by the materials that the water comes into contact with during the transportation from the tapping location to the water tap. Neither must the contact materials cause any kind of odour, discolouration or make the water cloudy or foamy.
The above requirements may seem rather obvious, but still over time it has been necessary to create a number of regulations concerning the quality – summarised in “Taste and odour”.
An example of a taste and odour test
In AVK GUMMIs R&D department, taste and odour tests are an integral part of the test programme when we develop new compounds for drinking water contact. During this process, we compare two water samples; one with rubber and one blank.
The test supervisor makes the following preparations:
The two bottles are placed in a dark cabinet for 72 hours at room temperature. After that, the odour of the water in the two bottles is compared. If the result is satisfactory, the taste of the water is then compared.
The test is carried out by three persons, randomly picked out from a test panel that have been approved for the test procedure. Each member of the test panel evaluates the test after which the average result is calculated.
What may cause taste and odour in a rubber compound?
A rubber compound consists of different ingredients of which the polymer is the most important. EPDM is typically used for contact with drinking water, among others because this type of polymer will release significantly less taste and odour than many other polymers, such as NBR and SBR. Again, EPDM may be subdivided into a number of types, each of which may have no or some taste and odour.
Apart from polymer, a number of fillers are added – some to improve the properties of the compound, others to reduce costs. Unfortunately, the most cost-efficient fillers have a tendency to release taste and odour, partly due to impurities.
Plasticisers are used to adjust the hardness and also to contribute to the homogenising of the compound. Plasticisers cover a number of chemicals, some of which are prohibited or unwanted as they are harmful to human health or the environment. Phthalates and aromatic mineral oils are examples of such chemicals. Many years ago, AVK GUMMI decided to avoid these chemicals completely, and for drinking water contact we only use approved ingredients that are also used in foods or medical products.
The curing system is a combination of ingredients, the purpose of which is to create cross-linking between the polymers to enable a flexible structure. The ingredients used may potentially release taste and odour, which means that is important to design a system that will result in the desired properties without releasing taste and odour.
The formulation of rubber recipes that not only comply with regulation, but also have the right chemical and mechanical properties without releasing taste and odour requires extensive know-how. This is a core competence that will always be important to the consumer, our customers and with that our company.