On social media and various news websites the rumor is spread that tap water can cause bladder cancer. NUcheckt investigated what is correct.

According to websites such as NineForNews , World Unity and Indignation, chemicals in tap water lead to thousands of cases of bladder cancer every year. However, the research to which these reports refer shows that tap water in the Netherlands is remarkably safe.

Where is it from?

The reports about bladder cancer and tap water are based on an international study published on January 15. This study looked at drinking water in 28 European countries.

Nicole Nijhuis, toxicologist at the KWR water research institute, explains that in many countries drinking water is treated with chlorine bleach to render pathogens harmless. Chlorine bleach is a cleaning agent that is often called bleach and is also used in some swimming pools. When water is disinfected with chlorine bleach, trihalomethanes are formed. Nijhuis writes that research shows that these substances may increase the risk of bladder cancer.

The January 15 study states that in many places in Europe there are indeed trihalomethanes in drinking water. Based on the concentration of trihalomethanes in the tap water, the researchers estimate that possibly 6,500 cases of bladder cancer in the 28 countries investigated were caused by this. However, many other things that also increase the risk of bladder cancer have not been taken into account in this study, Nijhuis emphasizes.

What about the Netherlands?

Moreover, the differences between countries are large. In Spain and the United Kingdom, the concentration of trihalomethanes is so high that, according to the calculation, more than 20 percent of bladder cancer cases are caused by these substances.

In the Netherlands, trihalomethanes would cause less than 0.1 percent of bladder cancer cases. If this theoretical calculation is correct, there would be four extra cases of bladder cancer in the Netherlands each year. However, it is unclear whether the concentration of trihalomethanes in Dutch tap water really increases the risk of bladder cancer.

Why no chlorine bleach in the Netherlands?

Nijhuis writes that the concentration of trihalomethanes in the Netherlands is very low in comparison with other European countries and more than meets the standards. This is because chlorine bleach is not standard used in the Netherlands for disinfecting water. Only in the event of an emergency is chlorine bleach added to the tap water if this is necessary for safety reasons.

Roberta Hofman-Caris, researcher drinking water treatment at KWR water, explains that the use of chlorine bleach is not standard required in the Netherlands, because there are far fewer leaks in the water pipes than in most other countries. Leaks in water pipes can be harmful, because clean water can be contaminated with pathogens through leaks.

In addition, the water purification companies disinfect in different ways. In most cases, according to Hofman-Caris, mainly UV disinfection is used, whereby possible pathogens are rendered harmless by means of UV light. No potentially carcinogenic substances arise.