Notes

Fresh water is not spread evenly across the Earth. Some places have much more fresh water than other places. For example, the Great Lakes in the midwestern United States are some of the world's largest freshwater lakes. They provide fresh water for millions of people in the United States.

Some places have very little fresh water. In some countries, people have to carry fresh water to their homes to drink, bathe, clean, and cook.

Almost all freshwater on Earth is found in two forms: groundwater and surface water. Most freshwater is found under the surface of the Earth as groundwater. Groundwater comes from rain or snow that has soaked into the ground. Once the water soaks into the Earth’s surface, it keeps sinking into the ground until it reaches a layer of rock that it cannot pass through.

A layer of Earth that holds groundwater is called an aquifer. People often get fresh water from wells that go into aquifers.

The top level of the groundwater in an aquifer is called a water table. The level of a water table is always changing. When it rains or snows, the water table rises. When people pump too much water out of the aquifer, the water table lowers. It is important for scientists to know the level of the water table because if it becomes dry, some people will not have water to drink!

Rivers have to start flowing from somewhere. A watershed is an area of land where all of the water in an area drains. The watershed often drains to form a river. If a watershed is polluted, it can pollute the water that flows into the river. If the river is polluted, it can pollute the water in all of the places that it flows, as well as the groundwater.