How Toxic Pipe Residues End up in our Drinking Water

Published on 11/10/2022 Last updated on 12/02/2024

New techniques and industrial advances mean that over the years different materials have been used to transport our drinking water from A to B. However, some of these materials have turned out to be less reliable than previously thought, causing toxic residues to leach into the water. Despite this, a large part of these pipelines are still in use today.

It is early 2020. The presence of toxic lead pipes in homes built before 1960 is on the news all the time. Melanie, Guido and their four children live in the Gentiaanbuurt in Amsterdam North. Since their home was built before 1960, the couple decides to test the tap water for lead. They find out that their water contains 115 micrograms of lead per litre. That is 23 times higher than the legal standard, which came into force in 2022, of 5 micrograms per litre.


Melanie has lived in the house for 18 years and has drunk many litres of tap water every day. After the discovery, the family books a medical check-up. The fact that lead endangers health is well known. According to research from the University of Florida, lead is particularly harmful to foetuses and children under 7 years of age. Although it is difficult to confirm a direct link, Melanie tells city broadcaster AT5 that she has had 4 miscarriages in recent years.

To transport water, pipes are necessary. In the past, it wasn’t clear whether the materials used could be harmful. However, the Romans, who were the first to use lead for their water pipes, suspected that lead could cause health problems. Despite this, it wasn’t until 1960 that lead was banned in hydraulic engineering. Over the years, different materials have been used to transport water. The very first Dutch water pipes, installed in 1853, were made of cast iron. Later, cast iron pipes were also found to release toxic substances into the water.

Polycyclic Aromatic Hydrocarbons

Many of the cast iron and steel pipes that were laid between 1900 and 1990 can release polycyclic aromatic hydrocarbons (PAH) into the water. This is because they are internally coated with bitumen and coal tar in order to protect the pipes against corrosion during storage. How long this kind of coating lasts varies a great deal. A study of 120 cast iron pipe sections found that the coating had completely disappeared in around 10 percent of the pipes, and that it was intact in just 30 percent.

Because of this coating, the allowable level of PAH stated in the Water Supply Decree can be exceeded. When this happens, the end customer notices quickly; the residues cause a change in the water’s taste and smell. During pipeline work, an extra layer of coating is sometimes added to protect the pipeline further. This too can deteriorate and end up in the water. As of 2017, there were still 8,977 kilometres of cast iron pipes and approximately 2,759 kilometres of steel pipes in the Netherlands. It is not clear how many of these were laid between 1900 and 1990.


The Health Council of the Netherlands has classified bitumen (both vapour and aerosol) as a suspected human carcinogen. Coal tar has been on the Ministry of Social Affairs and Labour’s SWZ List of Carcinogenic Substances for many years. The Watercycle Research Institute – commissioned by the Association of Dutch Drinking Water Companies – carried out a study into the coating of cast iron pipes and concluded that the amount of PAH in drinking water is small and does not pose a risk to public health.

The construction of asbestos-cement pipes has been prohibited since January 1993. Nevertheless, about 25 percent of the water pipe network in the Netherlands is made from this material. For years, asbestos has been linked to various types of cancer. Calcium hydroxide dissolves from the pipe wall, reducing the strength of the pipe and allowing asbestos fibres to leach into the water. Concrete and cement-based materials are now regulated. In 1974, researchers found the potential for asbestos residues to be a low risk to our drinking water. In 1999, Kiwa researchers thought the same.


Around 54 percent of the water pipeline network is made of plastics – either PVC (polyvinyl chloride) or PE (polyethylene). In areas affected by hard water, plastic pipes can actually benefit because limescale gets layered on the inside of the pipe, protecting the water from any residues. However, pipes made of PVC or PE can allow toxic substances from the soil to leach into the water (permeation). For example, there have been incidents in the past with methylbromide, an agricultural pesticide used to kill rats, insects and fungi. Small amounts ended up in drinking water and constituted a health hazard.

Figure 2: Graphic of a PE drinking water pipe and the processes that affect the degree of permeation. A distinction is made between the partition between the groundwater and the PE pipe, the diffusion of the contaminants through the PE wall and then the partition between the PE pipe and the drinking water. 

To prevent corrosion in water pipes, it is important to use the right materials. In the last few decades, there have been major developments in this area. Products and materials that come into contact with drinking water or are used in the preparation or purification of drinking water must not release substances into the water in quantities that have an adverse effect on health. Requirements for this were laid down in 2011 in the Regulation on materials and chemicals for drinking and hot water supply.

Water Treatment

Drinking water companies want to maintain their water transport network. They do this by maintaining the pipes, but they can also do this by adjusting the water’s composition: “conditioning”, or treating, the water. Drinking water has been conditioned on a large scale in the Netherlands since 1985. Water companies use the recommendations from 1988 to do this. In 2013, Kiwa Water Research (KWR), in consultation with Dutch drinking water companies, revised these recommendations. The changes are based on regulatory developments, research and industry experience.

Different materials are also found within our houses, of which there are about 6 million in the Netherlands. It is estimated that 90 percent of these consist of copper pipes with brass parts, such as taps and fittings. Copper pipes always leach copper into the water, to a greater or lesser extent. Our body needs copper for the formation of connective tissue and bones, proper functioning of the immune system and blood clotting. Too much, however, can cause irritation to the intestinal lining and mucous membranes, resulting in nausea, vomiting or diarrhoea. That said, the chances of consuming too much copper are small.


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