Don't Get Stuck Without Hot Water!
Just last summer I walked down stairs and stepped into a large puddle of water. I followed the water and realized it was coming from my water heater - a few common fail areas had indeed failed seemingly all at the same time and I realized I had a small crisis on my hands, no hot water. It was a good brand and just one year outside of it's warrantied date, so it wasn't some ancient relic. Hot water heaters are silent workhorses that seem like they'll last forever - until they don't. Hopefully when yours goes, it wont be catostrophic.
When a water heater finally throws in the towel, it can be as uneventful as a surprisingly cold shower or as damaging as unleashing its water contents all over your utility room, causing massive collateral damage. Fortunately, there are easily observable signs of failure that you as a homeowner can look for on a regular basis, easily preventing disaster!
Inconsistent Temperature
Most home hot water tanks aim to keep internal fluid temperature somewhere between 120 and 140 degrees Fahrenheit, an ideal temperature range for a broad range of applications from showers to washing dishes. If your water heater is unable to maintain this water temperature consistently, check what your water heater's thermostat is set to.
If it is set correctly (somewhere inside of the ideal temperature range) and still provides water at an inconsistent temperature, it could be a sign of a broken heating element. One key point to remain aware of is that too high OR too low of a water temperature are both indications of heating element failure, so don't just compensate for a higher-than-normal water temperature by adjusting the thermostat lower than it should be!
Abnormal Noises
Many homes make strange noises over the course of their lifetime. This can be caused by building materials settling or an operational sump pump and is perfectly normal.
One appliance that should NOT be making strange noises, however, is your water heater. If an aging water heater is producing loud creaking or knocking sounds it can be a sign of internal corrosion. When internal debris comes into contact with the water heater's heating element, these noises are produced as the sediment is quite literally burned away.
If you routinely hear noises coming from your water heater, hire a contractor to flush the tank for you and check your internal tank lining or sacrificial anode rod (if your water heater has one) for damage. If the internal tank lining is damaged, it is a good sign that it is time to replace your water heater. As an aside, if you are in the market for a new water heater, consider a tankless model. Among many other benefits, a tankless water heater completely avoids the problem of sediment buildup as it retains no domestic hot water within itself.
Leaks
This may seem like a trivial sign to check for, but small leaks can often go unnoticed, or are brushed aside as condensation or splashes from an external water source. If you discover a leak, no matter how small, call a contractor immediately to check for internal damage or corrosion.
Out of all the wear and tear that can happen to a water heater with long term use, leaks are the most dangerous, as even a small hole is a structural weakness that can cause the tank to tear itself open, damaging other areas or appliances in your home. Therefore, even a small hole is an immediate indication that replacing your water heater is necessary.