It depends how large you mean. The biggest areas are called oceans, slightly smaller than that are seas, then it is rivers, then lakes.
A large area of water is an ocean.
Oceans
An ocean.
A water catchment area.
lake
puddle
it is the ocean or a sea
Rain.
Ocean or sea.
Oceanologists
A water catchment area.
The ancient Romans called any large open area a campus. An example is the Campus Martius at Rome.