A brook is a very small, running stream of fresh water. Brooks often come from a spring.
A canal is a watercourse that has been made by people rather than a natural watercourse. Canals are generally cut to make a transportation path, for boats to travel along.
A channel is a waterway, or a path that has been worn by water. Channels can be so large you can't see the other side, or quite small, like a gutter by the side of a road. The picture is of a channel that has been worn into the rock by the waves of the sea.
A dam is a large wall built across a river to change the natural flow of water and make a deep lake form behind the wall. The water from dams is often used to water farm or supply water to a city, or to make electricity.
A drain is a type of hole, usually attached to a drainpipe, where water can escape from somewhere like a bath, washbasin or road. The entrance to a drain is usually covered by a grate. You can use the word drain to describe the process of the water leaving somewhere, or the hole through which the water escapes.
Gutters are channels that are used to carry water away to somewhere else. Gutters can be found around the edges of a roof, to catch the water and take it to storage or into a drain. Gutters are also found at the edges of roads, and sometimes also in the center of a road, to carry water away from the surface of the road.
A harbor, also spelt harbour, is a sheltered body of water that is deep enough for ships to dock and unload. Harbors are generally an inlet or bay surrounded by land. A harbor is also a term used for any safe place, or can be used as a verb to mean keeping something or someone safe, as in "he was harboring a known criminal".
A lake is a very large amount of water, usually in a valley in the mountains. Some lakes form in a crater where a meteor has hit. Most lakes are fresh water, some lakes near the sea may be salt water. A very very small lake in a park or a backyard is called a pond.
The ocean is the vast expanse of salty water that covers most of the Earth. Another word for ocean is sea.