Water company Vitens has advised local users in Gelderland to boil their drinking water before use to kill a bug found in one of its water reservoirs.

Some 46,000 households in Zevenaar, Didam, Dieren and the surrounding area are affected and have been told to boil the water for three minutes following an alert about the presence of the enterococcus bacteria, which can cause stomach upsets.

Viens said the contamination was “slight” but that the bug can be dangerous for people with a compromised immune system.

The reservoir, at Ellecom near Dieren, feeds other reservoirs, a spokesman for Vitens told local broadcaster Omroep Gelderland .

“Those reservoirs have not been affected but we did not want to take the risk and that is why we included the surrounding area in the warning as well,” he said.

All water that is consumed should be boiled for three minutes, including the water to brush teeth with and water given to pets.

Babies should not be given water at all, Vitens said, and bottled water should be used to make formula.

The problem is not new to the region, Omroep Gelderland said. Last August enterococcus was found in a reservoir in Didam and 7,000 people were told to boil their drinking water.

It is unclear how the enterococcus, which is usually found in human feces, ended up in the Ellecom reservoir. Vitalis has not said how long the warning will stay in place.