Boil water advisory in Amersfoort extended 11 days amid persistent intestinal bacteria

Residents of Amersfoort and surrounding areas have been advised to boil tap water for three minutes before drinking since January 5, as water tests continue to detect enterococci bacteria. The advisory, now in effect for more than 11 days, affects a larger area than a similar outbreak during the Christmas holidays, which lasted six days in a smaller part of the city.

Water company Vitens said the advisory will remain until multiple tests show the bacteria is no longer present. “It is a very persistent bacterium that is very difficult to remove from the water network,” a Vitens spokesperson said. “We flush and isolate clean sections of the network to make sure the bacterium cannot spread.”

Over the weekend, Vitens identified a potential source of contamination: a water storage cellar in Amersfoort. The facility was drained, cleaned, and taken out of service, but tests continue to detect enterococci elsewhere. Vitens emphasized that testing takes time. “Enterococci grow slowly. Only after two days can a reliable count be obtained,” the company said on its website. Multiple consecutive clean test results are required before lifting the advisory. An update is expected on January 20.

Residents have adapted to the prolonged advisory. Maarten Bouterse, a local resident, told NOS he has developed a daily routine using pots and water bottles.

Some residents have questioned whether boiling is necessary, given that enterococci naturally occur in human intestines and are generally harmless to healthy people.

Roberta Hofman, a water treatment researcher at KWR Water Research Institute, said boiling remains important. “Testing usually looks for two bacteria, enterococci and E. coli, because they are common and easy to detect,” she explained. “If those are present, it is likely that more dangerous bacteria could also be in the water.” She also discouraged switching to bottled water unless absolutely necessary, citing higher costs, greater environmental impact, and stricter monitoring of tap water compared with mineral water.

Hofman said the standard for dangerous bacteria allows only one in 10,000 people to become ill, meaning the presence of indicator bacteria like enterococci is closely monitored. Even these bacteria can pose a risk to people with weakened immune systems. “You want to prevent serious illness and maintain trust in drinking water,” she said. Boiling is only needed for water consumed or used for oral hygiene. Cooking water, such as for beans, is already heated longer, and showering does not pose a risk, Hofman clarified.

Vitens continues to search for the contamination source. “They have detected the bacteria several times. That means they must investigate the cause and ensure it is resolved,” Hofman said.