A cavitation device is provided for use in a method for the treatment of water by cavitation. The water to be treated passes through an annular cavitation zone which exists between two mutually opposite annular structures which rotate relative to one another and which have teeth directed substantially axially towards one another. Here, the water flows along cavitation surfaces which are provided on the face sides of the teeth of a first of the two annular structures and which are inclined in the circumferential direction such that, viewed in the relative direction of rotation of the other, second annular structure, the spacings between said teeth and said second annular structure increase.