As the biggest hot water tank may hold hundreds of litres, you'll want to take action as soon as possible if you encounter a leak. Why is this tank leaking in the first place, and what should you do next?
If you are sure that your tank is actually leaking and it's not just condensation on the outside, you need to take action. Turn the power off by flipping the breaker and then shut off the cold water supply.
Inlet And Outlet Pipes
Next, see if you can find the source of the leak. If it seems to be coming from the top of the tank and rolling down the side before pooling on the floor, the issue may be related to the pipes that supply the water. Here you will probably find two pipes. One will be the supply and the other one the outlet for the warm water you will use in your shower. Do the fittings or connections appear to be loose? If so, and you have a pipe wrench on hand, you could attempt to tighten them, but be very careful not to overtighten or apply too much pressure in any event.
Faulty Relief Valve
On the side of the tank, you will probably find the pressure relief valves. Is water coming from this area? A certain amount is to be expected as this is a safety feature that can release some water if the pressure within the tank is too high. If the settings are correct and in line with the manufacturer's recommendation, you may have a faulty valve, and it will need to be replaced.
Loose Drain Valve
On the bottom of the heater is the drain valve. A plumber will typically open this valve to evacuate all the water from the heater before maintenance. If water appears to be coming from this valve, check to see if it is tight but again, be careful that you do not break anything.
A Bigger Problem
If these aforementioned areas appear to be okay but you still have a growing pool of water on the floor, the tank may be cracked. While this is unusual, it's not unheard of, and you need to take action right away to fix the matter. You should get on the phone with an emergency plumber and see what they advise. They'll take a look and isolate the issue before recommending what to do next.