Drinking Water Materials Testing for WRAS Approval – BS 6920 Testing

The importance of drinking water materials testing

In the United Kingdom (UK), water regulations and bylaws require a water fitting to be of an appropriate quality and to not cause waste, misuse, undue consumption, or contamination to the water supply. Non-metallic materials that come into contact with water for human consumption are also required to comply.

These requirements may affect municipal water systems, pipes, commercial and residential water systems and even home appliances.

Understanding WRAS and BS 6920

Overview of BS 6920 standard

The British Standard 6920 (BS 6920) is used to evaluate the suitability of non-metallic products for use in contact with water intended for human consumption in regard to their effect on the quality of the water.

What is WRAS and the importance of WRAS approval?

The Water Regulations Approval Scheme (WRAS) is an independent approval body for plumbing products and materials.

Earning certification from WRAS helps manufacturers demonstrate that a material is of a suitable quality and has been tested to demonstrate compliance with the BS 6920 standard.

Steps in the testing process for BS 6920 certification

The following testing methodologies are part of BS 6920, in which samples are compared to controls to measure various characteristics of water that has been in contact with the products being tested.

Odor and flavor test

• Submersion in chlorinated and chlorine-free water
• Assessment of samples for discernible odor
• Assessment of diluted extracts for flavor

Color and turbidity, or appearance of water test

• 24-hour submersion of non-metallic material in test water
• Assessment of extract for color and turbidity for Hazen units (HU) for color and Formazine Nephelometric units (FNUs) for turbidity

Growth of aquatic microorganisms test

• Submersion of non-metallic material in water (up to 9 weeks)
• Measurement of the dissolved oxygen concentration during the fifth to seventh weeks of test
• Calculation of the mean dissolved oxygen difference (MDOD) value

Extraction of substances that may be of concern to public health (EXS), or cytotoxicity (Cyto) test

• 24-hour submersion of the sample material in water
• An extract is used to prepare a growth media for part two of the test, in which live cells are introduced
• Comparison (after a set period) of the cells against control samples in a blank and toxic (zinc sulfate) environment
• Analysis of the toxicity of the samples
• Additional testing if the morphology of the cells is affected in any way

Extraction of metals test

• 24-hour submersion in test water
• Measurement of the concentration of elements (those of potential concern to public health) in sample extracts (up to seven)
• Assessment of detected levels of concentration, with a reagent blank as a test validation