There are various causes of water damage such as leaks, clogged drains and building problems. A busted supply line/leaky pipe, a leaky roof, overflow of water from a sink or bath tub, and the breakdown of a machine that carries water are some factors.
The initial and very vital step to begin when you see a leak is to shut off the water. If turning off the water on the machine that is leaking doesn't work, or you're not sure where the water is leaking from, and then shut off the major water valve. It should be situated where cold water enters your home, inside in colder climates and outside in warmer climates.
After taking some vital care steps you must look around to make sure no other area is affected. Water has a way of getting around without being seen. If the leak happened upstairs, go downstairs and verify your ceilings and walls.
You need to contact a water damage restoration expert to come and take a look at the affected area. If the leak was small and easy to control, there is no need, but if the leak was large and may have sunk into the floors or walls then it is vital to make sure damage isn't still being done to your house.