Abstract: The invention relates to a device for purifying water, in particular for the continuous purification of water in the paper industry, said device comprising at least one supply line and at least one drain line for the water. The device also comprises a compression device for at least one sub-stream of the water, an injection device for injecting at least one gas and an expansion device for expanding at least one sub-stream of the water. In addition, the device comprises a unit for separating different phases of the water for purification. The device is characterized by a control system, which detects at least one parameter of the water and controls at least the addition of at least one additive in accordance with the process parameter.