Final answer:
A non-grounded receptacle located within 6 inches of water should be replaced with a GFCI to prevent electric shock by detecting and protecting against leakage currents.
Step-by-step explanation:
A non-grounded receptacle within 6" of water should be replaced with a Ground Fault Circuit Interrupter (GFCI). Replacing it with a GFCI ensures safety by detecting and protecting against electrical leakage currents that may occur when electrical devices are used near water. This protective device compares the current in the live/hot and neutral wires, and if an imbalance is detected, indicative of a leakage current, the GFCI will trip and interrupt the circuit.
This measure is crucial because a leakage current could return to the voltage source by a path other than the neutral wire, possibly through a person, which presents a serious electrocution hazard. The GFCI is designed to trip and cut off power if the leakage current is greater than 5 mA, which is considered the maximum harmless shock that a human can endure. It's a proactive safety feature to prevent electric shock and is particularly important for outlets near water sources.