2 Water on EarthWater is a dominant feature on Earth’s surface and is essential for life.Salt water and freshwater make up Earth’s water supply.In the water cycle, water circulates from Earth’s surface to the atmosphere and back again.Water plays an important role in people’s lives.
3 Salt water and freshwater make up Earth’s water supply. Water covers some two-thirds of the planet.Earth’s WaterAbout 97 percent of the Earth’s waterUnsafe to drink because of high levels of saltIn general, found in Earth’s oceans, which cover some 71 percent of the planet’s surfaceAlso found in some of Earth’s lakesSalt WaterWater without saltMakes up only 3 percent of our water supplyFreshwater
4 FreshwaterMuch of Earth’s freshwater is locked in glaciers, large areas of slow moving ice, and in the ice of the Arctic and Antarctic regions.Surface water is water that is found in Earth’s streams, rivers, and lakes.Less than one percent of Earth’s water supplyStreams, rivers, and lakes are common sources.Precipitation is water that falls to Earth’s surface as rain, snow, sleet, or hail.Most available freshwater is groundwater, water found below Earth’s surface.Some naturally bubbles from the ground to the surface as a spring.Most obtained by digging wells
5 The Water CycleWater is the only substance on Earth that occurs naturally as a solid, a liquid, and a gas, or water vapor.The water cycle is the movement of water from Earth’s surface to the atmosphere and back ; it is driven by the sun’s energy.Evaporation—water turns from liquid to gas.Condensation —the rising gas cools and condenses, or changes from a vapor into tiny liquid droplets, to form clouds.Precipitation —if the droplets in clouds become heavy enough, they fall back to Earth as rain, snow, sleet, or hail.Runoff —excess water that isn’t absorbed as groundwater flows over land and collects in streams, rivers, and oceans.
7 Water plays an important role in people’s lives. Water ProblemsLack of available freshwater, which can be caused by droughts or overuseContaminated, or polluted, water can harm humans, plants, and animals.Flooding can damage property and threaten lives.Water BenefitsProvides us with food to eatImportant source of energyProvides us with recreation, including swimming, fishing, surfing, and sailing