Usually, it is one of these four reasons for it leaking:
1. The Cold and Hot Water Inlet and Outlet Connections.
This is a very easy fix. Check the inlet and outlet pipe's connections and see if they are loose and causing water to leak. If this is the case, you may just need to tighten the connection with a wrench or replace a faulty pipeline.
2. The Temperature and Pressure Relief Valve.
The temperature and pressure relief valve is responsible for monitoring both the water temperature and pressure within a tank. If there is too much pressure in the tank, or the water becomes too hot, this valve will drain some of the water out of the tank. If this is the source of your leak, you will most likely be able to see water running down the side of your tank from the valve.
If this is the case, it could mean you need a new valve because the one you currently have is broken, or, it could also mean it is working properly and there is too much pressure in your water tank, so it is forcing water out through the T/P valve to prevent a bigger problem from occurring.
A licensed plumber can determine which one of these scenarios is the cause.
3. The Heater Drain Valve.
The drain valve is a standard but an easy issue to repair. If water is leaking from the valve, make sure it is closed completely. If this watertight drain valve continues to leak, you may have to replace it entirely, but it is relatively inexpensive.
4. The Bottom of the Water Tank.
The most common cause of a leaking water tank. When sediment builds up in the bottom of a water tank for years and years it will eventually corrode through the bottom of the tank and begin to leak. If age and deterioration is the cause of your leak, you will need to call a professional plumber to replace your water heater.
To avoid a major problem with your water heater… think preventative maintenance: