Water Authorities strive to maintain a high standard of drinking water for consumers and cannot afford to introduce any products or materials that may jeopardise water quality into their supplies. Consequently there is a need to ensure products that come into contact with drinking water do not carry or transmit substances that will cause this sort of deterioration.

A wide range of products and materials used in the water supply and plumbing industry are tested to the Standard, including coatings, gaskets, hoses, pipes (cement mortar lined for ductile iron pipes, fibreglass, plastic and steel), valves/backflow prevention devices, sealants and lubricants.

The Standard requires that products: do not affect the taste or appearance; do not support the growth of micro-organisms; and, do not release cytotoxic or mutagenic compounds or metals.

The Standard specifies that products intended for use in contact with drinking water be tested by exposure to extractant waters. The test surface area to volume ratio requirements are specified in the Standard. After the product has been exposed to test water, a sample of the test water extract is analysed to the requirements detailed in each appendix of the Standard.

Scaling factors or dilution factors can be applied to valves, backflow prevention devices and coatings used to line the interior of pipes or valves, reflecting the end use when used in a system; scaling factors are not applicable to pipes as they are tested to the ‘in-the-product’ exposure. In this method of exposure, the ratio of the exposed surface area to volume area ,to the extractant water volume in most cases will be equal to the surface area to volume ratio in end use.

The Standard considers products in contact with hot water where leaching of water-soluble compounds not detected in cold water applications can be evident in water extracts at high temperature.

The Standard investigates the following six parameters to determine a product’s suitability for contact with drinking water.

Taste of water

Concerns about the taste of drinking water generally produce the highest number of consumer complaints. A sensory test, in which trained taste panellists are provided with water extracts derived from a product, assesses the ability of the product to impart a discernible taste to drinking water.

Some materials are capable of leaching into water compounds, giving rise to unacceptable tastes.

Taste descriptors that may be encountered with plumbing materials include plastic/rubber/chemical/medicinal and may also be described in plastic piping and gaskets. Metallic/earthy/musty descriptors may be described with wholly metallic (stainless steel) or ductile iron/cement lined pipes.

Appearance of water

Consumers have an expectation that water supplied for drinking purposes appears clear and sparkling.

This test assesses the tendency of a product to impart a noticeable colour or turbidity to drinking water that would lessen its appeal. Extracts derived from a product are analysed by use of instrumentation to determine an increase in colour or turbidity. Some pigments and coatings can leach colours in water and certain metallic components can corrode and may affect turbidity.

Growth of aquatic micro-organisms

Non-metallic components including gaskets, coatings and o-rings are subjected to this test to determine whether or not they have the propensity to support the growth of aquatic micro-organisms by monitoring the dissolved oxygen levels in water extracts.

Drinking water often contains harmless micro-organisms; however certain organic compounds on a product’s surface can support the growth of organisms in a biofilm formation. In addition, this could lead to an increase in turbidity of drinking water and other issues relating to taste.

Cytotoxic activity of water

Certain product formulations may leach potentially toxic substances into water. These toxic compounds can be harmful to human intestinal cells. Mammalian cell lines are exposed to leachates derived from products to determine whether a cytotoxic reaction has occurred by observation of the cell line morphology.

Mutagenic activity of water

Mutagenic effect has been linked to potential carcinogens where an alteration to the genetic material of the cell has occurred. The Ames test is a reverse mutation assay that is used to determine whether or not products release mutagenic compounds into water extracts.

The extracts are exposed to specific bacteria, and a change in the nature of the bacteria is classed as evidence of mutagenic activity.

Materials in contact with drinking water should not produce any substances that alter the genetic material or genetic expression in cells.

Extraction of metals test

Many products that support a drinking water system contain metals in significant concentrations, either in low levels as with other compounds such as plastics, or as a residual from a manufacturing process.

This test assesses maximum concentrations for twelve metal elements in the extracts from products in contact with drinking water. The test assesses the ability of the product to leach metals as defined in the Standard.

In the past 15 years, the Australian Water Quality Centre, a business unit of SA Water, has tested over 3,000 products in accordance with the Standard. A large majority of these products tested are used to service the water piping industry. The products tested range from raw materials, as in resins used for composite pipes, to final products such as complete ductile iron cement lined pipes to valves and fittings.

It should be noted that similar products that are manufactured using different processes may exhibit different characteristics affecting the capacity of the product to leach compounds into drinking water.

The challenge for engineers, materials scientists and manufacturers is to produce commercially viable products that will not alter the aesthetics of drinking water or leach harmful compounds into it.