Water Resources of the United States

Water Distribution Demonstration

INTRODUCTION

Humans must have freshwater to live. But about ninety-seven percent of the Earth's water is too salty to use. The remaining 3 percent is freshwater, but most of it is in the polar icecaps, remote glaciers, and icebergs and is not easily accessible. Accessible freshwater, therefore, comes from streams, lakes, and underground sources. These sources represent less than one-half of one percent of all water on Earth. If all of the water on Earth equals 100 percent, then the following table shows the breakdown representing each type.

Earth's Total Water Supply	Earth's Total Freshwater Supply
97.2% Oceans (saltwater)   2.8% Freshwater ----- 100.0% Total Water on Earth	2.380% Icecaps, glaciers 0.397% Ground water 0.022% Surface water 0.001% Air and soil ------ 2.800% Total Freshwater on Earth

OBJECTIVES

After the demonstration, students will:

1. Know the distribution of Earth's water.

2. Be able to name the sources of freshwater on Earth (icecaps and glaciers, ground water, surface water, atmospheric water vapor, and soil moisture).

MATERIALS

Two 1,000-milliliter (mL) graduated cylinders, four 100-mL graduated cylinders, one medicine dropper, food coloring.

TEACHER PREPARATION

If two 1,000-mL graduated cylinders are not available, other clear containers can be used. If you have access to laboratory glassware, fifteen 100-mL graduated cylinders will work. Ten cylinders will hold 972 mL of saltwater, while the remaining five graduated cylinders will hold freshwater. A clear plastic jug holding one liter (soft drink container) of colored water can be used. Other clear glasses or jars can hold the smaller divisions. The following table shows the distribution of water for this demonstration: