A water treatment system including a UV bulb, a moisture detector, and a control circuit responsive to the moisture detector to terminate power to the bulb when moisture is detected. The moisture detector includes a nonconductive substrate and a pair of conductors on the substrate. When moisture is not present, the detector is nonconductive. However, when moisture accumulates on the detector, the moisture provides a conductive path between the conductors so that the detector becomes conductive. When moisture is detected, the control circuit terminates power to the bulb and/or provides an appropriate indication to the system user.