Where is Earth’s fresh water? About 97 percent of Earth’s water is salty ocean water, which cannot be used for drinking or watering crops. Only 3 percent of Earth’s water is fresh water. Most of that is ice. One quarter of Earth’s fresh water is liquid. Most of that liquid water is groundwater, the water stored in soil and rock beneath Earth’s surface. Surface water is found in rivers, streams, lakes, and ponds. It makes up less than one percent of Earth’s water supply. 1. Identify Where would you find the largest supply of liquid fresh water on Earth?

What is a watershed? A watershed is the land that supplies water to a river system. When a smaller river flows into a larger one, the area it drains becomes part of the larger river’s watershed. Because the Missouri and Ohio rivers flow into the Mississippi, the lands they drain are part of the Mississippi’s watershed. A ridge called a divide separates watersheds. Streams on each side of the divide flow in different directions. 2. Draw Conclusions Is a city on the Ohio River in the Ohio or Mississippi watershed?

How can human activity affect surface water in a watershed? Water shortages occur when people use water faster than the water cycle can replace it. Some areas never receive enough rain to meet their water needs. Wastes produced by agriculture, households, industry, and mining can result in water pollution. Sources of pollution include: Animal wastes, fertilizers, and pesticides from farms Untreated household sewage Industry and mining wastes Sediments, oil, and gasoline carried by runoff Heated water from factories and power plants (contd.)

Lakes and ponds can be polluted in the same ways as rivers and streams Lakes and ponds can be polluted in the same ways as rivers and streams. In addition, pollution can speed up eutrophication, a natural process in which nutrients build up over time. Dead organisms decay and release nutrients. These nutrients are food for algae, which form a layer on the lake’s surface. The thickening layer of algae blocks sunlight, killing plants. Decaying plant material builds up on the lake bottom. As the area fills in, land plants grow in the mud. Over time, a meadow replaces the lake. 3. Draw Conclusions Agricultural wastes sometimes include fertilizers, which are nutrients that aid plant growth. How might these wastes affect a pond?

How can human activity affect groundwater in a watershed? Any underground layer of permeable (little openings that allow gas and liquid to pass through) rock or sediment that holds water and allows it to flow is an aquifer. In the saturated zone, all underground spaces are filled with water. The water table is at the top of the saturated zone. The area above the saturated zone, where air fills the empty spaces between soil and rock, is the unsaturated zone. People withdraw groundwater for drinking and other uses through wells drilled into an aquifer’s saturated zone. (contd.)

Underground storage tanks, septic tanks, landfills, and chemicals poured on the ground can contaminate aquifers. Aquifers that become polluted do not recover quickly. If people take water from an aquifer faster than the aquifer refills, the level of the aquifer will drop. Withdrawal of large quantities of water from an aquifer can also cause the land above it to sink. Along coasts, heavy withdrawal of fresh water from aquifers allows salt water from the ocean seep in and contaminate wells. 4. Draw Conclusions What would happen to the saturated and unsaturated zones of an aquifer during a long drought? What might happen to shallow wells?

Grab a piece of copy paper and draw the two diagrams below, they should be on the same side of the paper.

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