There are many possible causes of water leaking from the water heater. It could be due to one reason or several. It is rare for multiple problems to happen at the same time but not unheard of. The causes can be rather simple or they can be quite complex.
Simple causes of water leaking from the water heater would be faulty materials or a small component malfunctioning. The water heater may not be ideally balanced or leveled. The nuts and screws may not be tightened enough. The inlet and outlet may have leaks. There can be dents or cracks. All such cases will come under warranty if you are still within that period. Installation problems can also cause water leaking from the water heater but that is not a simple problem. You may not be able to figure out the actual cause owing to installation issues. You must call in the installation guys or get a local plumber to check for possible problems.
In most cases, water leaking from the water heater is due to installation errors, a faulty water heater where one or more components are not working properly, valves failing to do their job or an extremely high temperature setting which will result in a pressure that the temperature-pressure relief valve is unable to withstand. Not all leaks are equally concerning. Some leaks are good because the water heater is programmed to let out some water when it is beyond capacity or overheated.
You need to check where the leak has originated. If you see water dripping from the sides of the water heater, then don’t presume that is where the leak is. It could be at the top. When you find water leaking from the bottom, don’t presume the problem lies there as it could very well be water dripping from the top by the sides and then appearing to drip from the bottom. Delve extensively to inspect the source of the leak. This will be partly influenced by the model of water heater you have. Not all heaters have the inlets, outlets, and valves at the same place.
Whether it is the drain valve or the temperature-pressure relief valve, whether it is an installation error or a worn-out component, it is best to call in an expert. Unless you are an expert yourself, diagnosing and fixing the problem of water leaking from the water heater can be quite daunting.