There are several signs that a water heater is failing; however, a puddle forming under the unit is a sign of imminent failure. The water indicates the tank is leaking. American Family Insurance recommends calling a plumber immediately to prevent the tank from bursting or flooding the room where it is located. The water and power or gas to the tank should be turned off until the plumber arrives.
Careful observation may give a homeowner an indication that a tank is ready for replacement earlier. If the water is no longer as hot as it once was or the unit takes longer than normal to heat, there could be a developing problem. Loud pops or cracks often indicate a build up of lime or scale on the heating element or the inside of the tank. While heating elements are replaceable, a reputable plumber usually checks the integrity of the tank before replacing them.
The water coming out of the tank often provides other clues. As the metal starts to break down, it undergoes chemical reactions with the water. Users often note a rotten egg smell from sulfur compounds that form in the water, see rust stains on their laundry or find the water has an odd taste. Such clues indicate it is time for the device to be serviced or replaced.