The UN humanitarian agency said Monday that they had been working for Hydraulique Sans Frontieres.
The attack took place in the village of Mushikiri in Congos North Kivu province.
While there was no immediate claim of responsibility, the Mai Mai militia is known to be active in the area.
In a statement, the UN humanitarian agency says worrisome security conditions in North Kivu province are hindering efforts to help the thousands in need there.