Leak in aging storage cellar likely caused Amersfoort water contamination this winter

Two drinking water boil advisories affecting tens of thousands of households in late 2025 and early 2026 were likely caused by a leak in a drinking water storage cellar at Vitens’ production facility on Hogeweg, the company said following an investigation.

Vitens said the contamination in the Amersfoort region, detected at the end of December 2025 and again in early January 2026, was most likely linked to aging concrete in the storage cellar, which allowed outside water, such as rainwater, to enter the system.

In both cases, the problem was reportedly a small amount of enterococci bacteria, which are germs that usually live in the intestines of people and animals and can indicate that the water is contaminated with feces.

Vitens said the storage cellar, where drinking water is held before distribution, contains sections of aging concrete that made it more vulnerable to external influences. “A leak through the concrete is the most likely cause of the contamination,” the company said, adding that the cellar will not be used for now and will be renovated before returning to service.

The investigation included a full building inspection by an external specialist firm as well as internal technical assessments and evaluations.

Vitens said identifying the cause took time because bacterial concentrations were low. During the contamination events, technical teams reportedly worked day and night to clean and flush the water distribution network in order to restore water quality as quickly as possible.

Alongside the operational response, Vitens conducted extended research to determine the source and required solutions, ultimately concluding the storage facility was the most probable origin.

The company also reviewed its handling of the second boil advisory and acknowledged problems in customer communication. It said information was in some cases released to the media before reaching customers directly. In addition, an online postcode checker used to determine whether households were affected became temporarily unavailable due to heavy website traffic.

Vitens said it is implementing changes, including upgrades to its website to handle high visitor volume and a review of customer data systems and regional segmentation.