Leaks interfere with water heater efficiency and also represent health hazards. Below are some of the reasons your water heater might leak.
A typical water heater has two water pipes; the cold (inlet) and the hot (outlet) water pipe. Over time, either of these pipes can loosen and leak water. The leaking water may flow down the sides of the tank and collect on the floor. If this is the only problem with your tank, then the solution is as easy as tightening the loose pipe with a wrench.
Damaged Relief Valve
When the water inside the tank heats up, its pressure also rises. The water heater system is designed to handle a wide range of temperature and pressure, but there is no telling when the pressure inside the tank might exceed this limit. The relief valve acts as a safety measure if the pressure inside the tank gets too high. However, a damaged relief valve might leak even if the pressure inside the tank is moderate. In such a case, a replacement of the valve is warranted.
As mentioned above, the pressure release valve is meant to ensure your water heater is safe if the pressure inside the tank rises to dangerous levels. The valve does this by releasing some of the water inside the tank to relieve the pressure. Thus, if the pressure valve is leaking water, it can either mean that the valve is damaged or the pressure inside the tank is dangerously high.
A water heater technician should diagnose the issue and offer a solution. Don't just replace the relief valve before confirming whether the issue is high pressure or relief valve damage.
Damaged Drain Valve
A water heater drain valve, located towards the bottom of the tank, is useful from draining water off the tanks. For example, you may wish to drain water off the tank to clean, service, or replace it. The drain valve should be watertight the rest of the time. Thus, you should suspect that the drain valve is damaged if it is leaking water, but you haven't opened it. The drain valve may leak if it is damaged, say by corrosion, or if it is loose. You may have to tighten or replace the drain valve depending on the situation.
Lastly, your water heater may also leak if the tank is damaged and has holes or cracks. The bottom of the tank is particularly vulnerable to this kind of damage. After years of use, the accumulation of sediments in the tank may cause the bottom of the tank to corrode and develop holes. In such a case, the only solution is to replace the tank.
In many cases, it is not easy to know why your water heater is leaking. A professional plumber can help you diagnose and fix the damage before you run out of hot water or someone gets hurt.