An ice maker comprising a refrigeration system, a water system, and a control system. The control system includes a controller comprising a processor and a water level sensor. The water level sensor is adapted to externally sense a capacitance corresponding to a sump water level. The controller is adapted to control the operation of the refrigeration system and the operation of the water system based upon the sump water level and to detect one or more failure modes of the water system based upon the sump water level.