The Water CycleChapter 2.1

Seventy percent of the earth’s surface is covered with water.

There is water literally all around us in the form of water vapor, or water in the atmosphere in the form of gas.

The Water CycleDid you know that the total amount of water

on the earth’s surface does not change?Water constantly moves.Water goes from the oceans to the air to the

ground and finally back to the oceans.This is the water cycle.

EvaporationThe sun’s heat turns liquid water

into water vapor, or humidity.

Did you know that warm air can hold more humidity than cool air?

CondensationAs water vapor rises and cools, it

changes back into liquid in a process called condensation.

PrecipitationTiny droplets of water form clouds

and fall back to the earth in the form of precipitation—rain, snow, sleet, or hail

Precipitation soaks into the ground and collects in stream and rivers.

CollectionDuring collection, streams and

rivers carry the water back to the oceans.

Then the cycle begins again.

The water cycle

Fresh WaterOnly about 2 percent of the water found on the

earth is freshwater.Of that 2 percent, about 1.6 percent is frozen into

giant sheets of ice, or glaciers.Groundwater fills tiny cracks and holes in the

rock layers below the earth’s surface.There is 10 times more groundwater than there is

water in rivers and lakes.Some of this water flows through underground

rock layers called aquifers.

Salt WaterThe earth’s four major oceans—the Pacific,

Atlantic, Indian, and Arctic Oceans—contain salt water, which is not fit for human consumption.

Salt water is also found in seas, gulfs, bays, and straits.