An apparatus reminds an operator of a need to change water in a reservoir of a warewasher. A counter that counts operating cycles of the warewasher and a sensor provides signal indicating that the reservoir has been drained and refilled. A controller responds to the counter having a first threshold value by activating an annunciator to alert the operator that is it time to change the water. Thereafter when the counter has a greater second threshold value and the controller disables operation of the warewasher until the sensor indicates that the reservoir has been drained and refilled. Thus the operator is required to change the water in order to continue using the warewasher.