Faulty T&P (temperature and pressure) relief valve
T&P valve leak due to excessive pressure, overheating or stuck
Leak from overhead or nearby plumbing connection
Leaking water tank (corrosion likely)
Place bucket under overflow pipe. Open and flush T&P valve clear of debris. If leak remains from valve, replace valve.
Reduce thermostat setting to prevent tank overheating and opening T&P relief valve.
Inspect bottom of tank by looking through combustion chamber. If water marks or heavy rusting is noticed or if water is noticed setting in combustion chamber bottom, then the water heater needs to be replaced.