The Jura ENA8-X6-X8-Z6-Z8 Water Tank Level Sensor CPU detects when the proper amount of water is in the water tank. If there is water in the water tank, but the machine is prompting you to fill the water tank, then this part may be defective and needs to be replaced. Damage often occurs from water that is spilled out of the water tank when it is reinserted or from a leaking water tank.