A voltage gradient detector provides notice when a potentially hazardous voltage gradient is present in water, employing at least one pair of spaced-apart electrodes connected to an LED. The electrode spacing is selected such that, when exposed to a sufficiently large voltage gradient, the voltage between the electrodes causes activation of the LED. The LED can provide visual illumination, or can be a part of a switching device such as a photoMOS relay that in turn activates an alarm device such as an audible sounder or a high-intensity light. Sensitivity in multiple directions can be attained by employing a pair of LEDs between the electrodes, and by employing three pairs of electrodes and associated LED pairs, with the pairs of electrodes being spaced apart along substantially orthogonal axes. These pairs may be discrete or may share an electrode in common.