We live on a watery planet. Did you know that the oceans contain 96 percent of all the water on Earth? The water you use every day is not ocean water, though—that is too salty. Humans rely on freshwater, which only makes up about 2 percent of all the water in the world. (The rest of the water on Earth is included in the polar ice caps, glaciers, and places where snow does not melt.)
But we use a lot of water. Scientists estimate that people in the United States alone use 400 billion gallons every day, doing everything from brushing teeth to watering crops on a farm. Because of this, we could have shortages of water, energy, and other resources in the future. Can using math help us make decisions about how to protect these important resources?