There has been some recent publicity on the possibility of lead contamination from brass taps so we thought some more information on this issue would be helpful.
Brass is an alloy of predominately copper and zinc with small additions of lead (1.5 – 3.5%) which are added to the alloy to improve the properties of the material so it can be cast and readily machined into the taps we all know. Brass and other alloys can corrode and release very small amounts of metals when they are in contact with drinking water. Lead particles in the brass can dissolve into the water but the rate of dissolution or leaching depends on the brass alloy and the corrosivity of the water. The extent of the metal dissolution will depend on factors such as water quality, temperature and time of stagnation and can result in minute amounts of metals being leached into the water. Certainly for brass alloys very small amounts of lead can be leached into the water.
All components used in both water utility and domestic applications are required to conform to the requirements of the Australian- New Zealand Standard AS/NZS 4020 - Testing of products for use in contact with drinking water. This is a very comprehensive standard and involves a series of seven tests which are carried out in both hot and cold water. One of the tests is for assessing the leachability of metals where sample of the metal are left in contact with water for various lengths of time up to 72 hours after which the water is analysed for the presence of metals.
The standard recognises that plumbing and water supply systems are made up with different materials so the assessment of an individual component needs to be carefully considered in the context that it may be only a small part of the system. From a practical point of view the Standard adopts the use of scaling factors to ensure that the results are relevant and representative of real life situations and still safe to ensure the materials do not have any detrimental impacts to consumers’ health. The scaling factor determination can be quite complicated but for illustration purposes let’s consider a standard garden tap. The tap when closed has approximately 8-10 ml of water in contact with the brass and over time there may be some small amounts of lead which leach into that small volume of water. The maximum limits for lead in Australia and the rest of the world are 10 parts per billion (ppb) so let’s assume there was 20 ppb in that little bit of water in the tap. There’s no lead in any of the connecting pipe materials. If you run a glass of water (approx. 200 ml) from the tap, the water that was in contact with the brass will be diluted by 20 to 25 times so the amount of lead in that full glass of water would be less than 1 ppb – well below the 10 ppb maximum. This simple analogy is used for all products that are approved to be used in the water supply systems and ensures that there are no harmful materials that can contaminate the water to the detriment of consumers.
The water agencies and standards ensure that products used in the water supply do not contaminate drinking water. It’s unfortunate that the issue of lead leaching from brass wasn’t reported correctly causing unnecessary concern for consumers.
B App Science, Metallurgy. CMatp
ACA Corrosion Technologist