British Standard BS 6920
By Rick Andrew
Non-metallic materials in contact with drinking water in the UK must conform to British Standard (BS) 6920 to address regulations regarding prevention of contamination of the drinking water supply. Suitability of non-metallic products for use in contact with water intended for human consumption with regard to their effect on the quality of the water (the official title of BS 6920) may be long, but it does effectively describe the scope and purpose of the standard. BS 6920 includes five main test requirements, applied to all non-metallic materials in contact with drinking water:
- Odor and flavor
- Color and turbidity
- Extraction of metals
- Extraction of substances of concern to public health
- Growth of aquatic microorganisms
Interestingly, there is no safety standard or testing applicable to metallic materials in contact with drinking water in the UK. So non-metallic materials are evaluated for extraction of metals, along with the four other tests listed above, but metallic materials are not evaluated for extraction of metals in the UK.
Odor and flavor
This test is performed on individual materials to determine if the materials impart a discernible odor or flavor to the water. A taste test panel is employed for the evaluation. The test is conducted with both chlorinated and non-chorinated water. After exposure to the water and a 1:1 dilution is performed, both the chlorinated and non-chlorinated extracts must be free from flavor.
Color and turbidity
Evaluations are conducted on each material to determine whether they increase the color and/or turbidity of water to which they are exposed, using instrumental analysis methods. After exposure, any increase in the color or turbidity of the water must be less than five Hazen units and 0.5 FNU (Formazin Nephelometric Units), respectively.
Extraction of metals
A leaching test on all non-metallic materials is conducted. A set list of metals is analyzed regardless of material type or formulation. The list of metals and maximum admissible concentration (MAC) of each is included in Figure 1. Metallic materials are not evaluated under this test.
Extraction of substances of concern to public health
This test is also known as the cytotoxicity test. Materials are exposed to water and then the water is placed in contact with mammalian cells to observe any toxic effects on the cells, in order to assess potential human toxicity. This is a study of gross acute toxicity.
Growth of aquatic microorganisms
Materials are placed into water that is saturated with dissolved oxygen and sealed into bottles. Over a period of seven to nine weeks, the dissolved oxygen levels are measured to determine if any aerobic microorganism growth has resulted in a decrease in the level of dissolved oxygen in the water. The mean dissolved oxygen difference (MDOD) between water exposed to the product and control is determined based on measurements taken in weeks 5, 6 and 7. The MDOD must be less than 1.7 mg/L for the results to be passing. If after seven weeks the MDOD value is between 1.7 mg/L and 2.0 mg/L, then the test is continued for two additional weeks. If the final MDOD value over weeks 5, 6, 7, 8 and 9 is less than 1.7 mg/L, then the results are passing. If the MDOD value is 1.7 to 2.9 mg/L, then two additional product samples can be tested. If the arithmetic mean of the MDOD values from the three product samples is less than 2.4 mg/L, then the results are passing. If the MDOD is > 2.9 mg/L, then the test results are failing.
Products intended to be used in domestic hot-water systems or in other applications expected to see elevated temperatures can be tested to demonstrate compliance with the standard up to 85°C (185°F). The odor and flavor, color and turbidity, extraction of substances of concern to public health and extraction of metals tests are carried out at the specified high temperature. In addition, the odor and flavor and extraction of substances of concern to public health are carried out at 23°C (73.4°F). The growth of aquatic microorganisms test is always carried out at 30°C (86°F).
Note that each of these tests is conducted on one material only, not on products consisting of multiple materials. So, there will be multiples of each of these tests for products that include multiple non-metallic materials in contact with the water supply, with each being a separate test on separate materials. Note also that no formulation disclosure is required because the testing is applied in the same way for each non-metallic material regardless of material type or formulation. Ten samples of each material are required. Each of the ten samples must have a surface area of 15,000 ± 500 mm2, so there is enough material for all of the tests. A sample may consist of more than one piece. So for a small product or part consisting of one material, such as an O-ring, there may be many of them included in each sample to make up the 15,000 ± 500 mm2. The samples must also be no more than 12 months old at the date they are received at the test laboratory. When shipped to the laboratory, the samples are typically placed into labeled, polyethylene bags, because samples labeled directly (with adhesive tape, ink, etc.) are not acceptable.
WRAS approvals for the UK
Water Regulations Advisory Scheme (WRAS) itself is an independent organization, with membership comprised of representatives from 26 UK water supply companies. WRAS approval includes submittal of product information and test results to demonstrate conformance to the WRAS requirements. WRAS does not own or operate a testing laboratory. WRAS approvals for fittings require both mechanical testing, as well as testing of non-metallic tests to BS 6920. Mechanical test reports in accordance with WRAS requirements may be accepted from ISO 17025-accredited laboratories. Material-test reports according to BS 6920 must be from laboratories listed on the WRAS website at www.wras.co.uk. WRAS approves these laboratories based on their participation in comparison tests conducted to ensure that approved laboratories achieve similar test results.
Once the information is submitted, it is reviewed by the Product Assessment Group (PAG). The PAG meets about 20 times each year to review the recently submitted WRAS approval applications and make a determination regarding acceptance. If the application is determined to be acceptable, then the WRAS issues the approval. Each approval is added to the WRAS online Products and Materials Directory. This directory can be found at https://www.wras.co.uk/approvals/. Approvals are valid for five years. There are no manufacturing-facility audits required for WRAS approvals. Products achieving WRAS approval are authorized to use the scheme’s approved certification mark.
About the author
Rick Andrew is NSF’s Director of Global Business Development–Water Systems. Previously, he served as General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at (800) NSF-MARK or email: Andrew@nsf.org