Earth’s Fresh WaterEarth’s Fresh Water

Fresh WaterFresh Water

Oceans cover more than 70% of the Earth’s Oceans cover more than 70% of the Earth’s surface.surface.

97% is found in the oceans.97% is found in the oceans. Fresh water makes up only 3% of the Fresh water makes up only 3% of the

Earth’s water.Earth’s water. 85% of the fresh water is frozen in the polar 85% of the fresh water is frozen in the polar

icecaps.icecaps.

The The Hydrologic CycleHydrologic Cycle

The Hydrologic CycleThe Hydrologic Cycle

Most of the fresh water on the Earth’s Most of the fresh water on the Earth’s surface is found in moving and in stand surface is found in moving and in stand water.water.

Rivers, streams and springs are moving Rivers, streams and springs are moving water.water.

Ponds, lakes, and swampy wetlands are Ponds, lakes, and swampy wetlands are standing water.standing water.

Water CycleWater Cycle

The hydrologic cycle or water cycle is the The hydrologic cycle or water cycle is the movement of water from the oceans and movement of water from the oceans and freshwater sources to the air and land and freshwater sources to the air and land and finally back to the oceans.finally back to the oceans.

The water cycle constantly renews the The water cycle constantly renews the Earth’s supply of fresh water.Earth’s supply of fresh water.

Steps of the CycleSteps of the Cycle

EvaporationEvaporation CondensationCondensation PrecipitationPrecipitation

EvaporationEvaporation

The first step involves the heat energy given The first step involves the heat energy given off by the sun. This energy causes water on off by the sun. This energy causes water on the surface of the Earth to change to water the surface of the Earth to change to water vapor.vapor.

This process is called evaporation.This process is called evaporation.

Sources of EvaporationSources of Evaporation

Enormous amounts of water evaporate from Enormous amounts of water evaporate from the oceans.the oceans.

Water also evaporates from freshwater Water also evaporates from freshwater sources and from the soil.sources and from the soil.

Animals and plants release water vapor into Animals and plants release water vapor into the air.the air.

CondensationCondensation

The second step is condensation.The second step is condensation. Condensation is the process by which water Condensation is the process by which water

vapor changes back into a liquid.vapor changes back into a liquid.

CondensationCondensation

For condensation to occur, the water vapor For condensation to occur, the water vapor must be cooled.must be cooled.

This happens when the warm air close to This happens when the warm air close to the surface of the Earth rises.the surface of the Earth rises.

As it moves farther from the Earth, it cools.As it moves farther from the Earth, it cools. Cool air holds less vapor and it condenses Cool air holds less vapor and it condenses

into droplets of water known as clouds.into droplets of water known as clouds.

Water VaporWater Vapor

When water evaporates from the ocean, it When water evaporates from the ocean, it leaves the salts behind. leaves the salts behind.

Water vapor is made of fresh water only.Water vapor is made of fresh water only.

PrecipitationPrecipitation

The third step is precipitation.The third step is precipitation. Precipitation occurs when the water returns Precipitation occurs when the water returns

to the Earth in the form of rain, snow, sleet to the Earth in the form of rain, snow, sleet or hail.or hail.

PrecipitationPrecipitation

Precipitation occurs when the water droplets Precipitation occurs when the water droplets that form in clouds become too numerous that form in clouds become too numerous and heavy to remain afloat in the air.and heavy to remain afloat in the air.

It returns to the Earth as rain, snow, sleet or It returns to the Earth as rain, snow, sleet or hail.hail.

After it falls, some returns to the atmosphere After it falls, some returns to the atmosphere through evaporation and the cycle is through evaporation and the cycle is complete.complete.

GroundwaterGroundwater

Some of the water that falls as precipitation Some of the water that falls as precipitation may run off into land, ponds, streams, river may run off into land, ponds, streams, river or oceans.or oceans.

Some may soak into the ground and Some may soak into the ground and become groundwater.become groundwater.

At some point, the groundwater flows At some point, the groundwater flows underground to the oceans.underground to the oceans.

Frozen WaterFrozen Water

Snow is a frozen form of water.Snow is a frozen form of water. The pressure of piled-up snow causes some The pressure of piled-up snow causes some

of the snow to change into ice and of the snow to change into ice and eventually glaciers form.eventually glaciers form.

A glacier is a huge mass of moving ice and A glacier is a huge mass of moving ice and snow.snow.

GlaciersGlaciers

Glaciers form in very cold areas. Glaciers Glaciers form in very cold areas. Glaciers hold 2% of fresh water.hold 2% of fresh water.

Because of the extremely cold Because of the extremely cold temperatures, the snow that falls does not temperatures, the snow that falls does not melt completely. As more snow falls it do melt completely. As more snow falls it do covers the old snow. The pressure covers the old snow. The pressure squeezes the snow crystals together and ice squeezes the snow crystals together and ice forms. When the layer of ice become very forms. When the layer of ice become very thick and heavy, the ice begins to move.thick and heavy, the ice begins to move.

Valley GlaciersValley Glaciers

Long, narrow glaciers that move downhill Long, narrow glaciers that move downhill between the steep sides of mountain valley between the steep sides of mountain valley are called valley glaciers.are called valley glaciers.

Usually valley glaciers follow channels Usually valley glaciers follow channels carved by running water. The movement of carved by running water. The movement of the glacier downhill causes cracks in the ice the glacier downhill causes cracks in the ice known as crevasses.known as crevasses.

Valley GlaciersValley Glaciers

As valley glaciers slide downward, they tear As valley glaciers slide downward, they tear rock fragments from the mountainside.rock fragments from the mountainside.

The rock fragments become frozen in the The rock fragments become frozen in the glaciers and cut deep grooves in the valley glaciers and cut deep grooves in the valley walls. Mountains located anywhere from the walls. Mountains located anywhere from the equator to the poles can contain glaciers.equator to the poles can contain glaciers.

Mount Rainier in Washington and Mount Mount Rainier in Washington and Mount Washington in New Hampshire contain Washington in New Hampshire contain small glaciers.small glaciers.

MeltwaterMeltwater

As the valley glacier moves, some of the ice As the valley glacier moves, some of the ice begins to melt, forming a stream of water, begins to melt, forming a stream of water, called meltwater.called meltwater.

Meltwater is usually pure water and some Meltwater is usually pure water and some cities such as Boulder, CO use it as a cities such as Boulder, CO use it as a source of drinking water.source of drinking water.

Some meltwater is used to generate Some meltwater is used to generate electricity although it is costly and could alter electricity although it is costly and could alter the environment.the environment.

Continental GlaciersContinental Glaciers

In the polar regions, snow and ice have built In the polar regions, snow and ice have built up to form thick sheets, called continental up to form thick sheets, called continental glaciers.glaciers.

Continental glaciers cover million of square Continental glaciers cover million of square kilometers of the Earth’s surface. kilometers of the Earth’s surface.

They move slowly in all directions.They move slowly in all directions. Continental glaciers are found in Greenland Continental glaciers are found in Greenland

(85%) and Antarctica (98%).(85%) and Antarctica (98%).

IcebergsIcebergs

At the edge of the sea, continental glaciers At the edge of the sea, continental glaciers form overhanging cliffs. Large chunks of form overhanging cliffs. Large chunks of ice, called icebergs, often break off from ice, called icebergs, often break off from these cliffs and drift into the sea. Some these cliffs and drift into the sea. Some icebergs are as large as the state of Rhode icebergs are as large as the state of Rhode Island.Island.

Icebergs pose a major hazard to ships, as in Icebergs pose a major hazard to ships, as in the sinking of the Titanic in 1912.the sinking of the Titanic in 1912.

Fresh Water in IcebergsFresh Water in Icebergs

Much fresh water is frozen in icebergs. Much fresh water is frozen in icebergs. Attempts have been made to tow icebergs Attempts have been made to tow icebergs

to areas that need fresh water. to areas that need fresh water. There are problems with transporting There are problems with transporting

icebergs. First the effect of icebergs on icebergs. First the effect of icebergs on local weather must be considered. Second, local weather must be considered. Second, it would be costly and time-consuming. it would be costly and time-consuming. Last, ways are needed to stop melting.Last, ways are needed to stop melting.

Running WaterRunning Water

Rivers and streams are important sources of Rivers and streams are important sources of fresh water. Many towns and cities build fresh water. Many towns and cities build near rivers and streams.near rivers and streams.

The water is used to irrigate crops, generate The water is used to irrigate crops, generate electricity, drinking and other household electricity, drinking and other household purposes.purposes.

Rivers are also used for recreational Rivers are also used for recreational purposes.purposes.

Rivers have been used to remove waste.Rivers have been used to remove waste.

Surface RunoffSurface Runoff

Rain and melted snow that do not evaporate Rain and melted snow that do not evaporate or soak into the soil flow into rivers and or soak into the soil flow into rivers and streams. The water that enters a river or streams. The water that enters a river or stream after a heavy rain or spring thaw is stream after a heavy rain or spring thaw is called surface runoff.called surface runoff.

Amount of RunoffAmount of Runoff

The amount of surface runoff is affected by The amount of surface runoff is affected by several factors. One is the type of soil the several factors. One is the type of soil the precipitation fall on. Some soils are more porous precipitation fall on. Some soils are more porous and soak up more water. and soak up more water.

The condition of the soil is also important. Dry soil The condition of the soil is also important. Dry soil will soak up more. Wet soil will accept less waterwill soak up more. Wet soil will accept less water

Plant roots absorb water. In areas where there Plant roots absorb water. In areas where there are many plants, more water is absorbed.are many plants, more water is absorbed.

WatershedWatershed

A land area in which surface runoff drains A land area in which surface runoff drains into a river or a system of rivers is called a into a river or a system of rivers is called a watershed.watershed.

Water sheds prevents floods and water Water sheds prevents floods and water shortages by controlling the amount of water shortages by controlling the amount of water that flows into streams and rivers. that flows into streams and rivers.

Watersheds also provide a steady flow of Watersheds also provide a steady flow of fresh water into the oceans.fresh water into the oceans.

Usefulness of RiversUsefulness of Rivers

Many rivers are sources of fresh water. The Many rivers are sources of fresh water. The amount of water in a river and the speed at which amount of water in a river and the speed at which the water flows affect the usefulness or a river as the water flows affect the usefulness or a river as a source.a source.

Rivers that move quickly carry more water. They Rivers that move quickly carry more water. They also carry a lot of soil, pebbles and sediments. also carry a lot of soil, pebbles and sediments. Slow moving rivers appear more clear.Slow moving rivers appear more clear.

Pollution also affects the usefulness of a river.Pollution also affects the usefulness of a river.

Standing WaterStanding Water

Within a watershed, some of the surface Within a watershed, some of the surface runoff gets caught in low places. Standing runoff gets caught in low places. Standing bodies of fresh water are formed there.bodies of fresh water are formed there.

Depending on their size, these bodies of Depending on their size, these bodies of water are called ponds or lakes, which water are called ponds or lakes, which provide fresh drinking water.provide fresh drinking water.

Surface runoff keeps the ponds and lakes Surface runoff keeps the ponds and lakes from drying up. The ponds and lakes from drying up. The ponds and lakes control flooding and hold water in reserve.control flooding and hold water in reserve.

LakesLakes

Lakes are usually large, deep depressions Lakes are usually large, deep depressions in the Earth’s crust that have filled with fresh in the Earth’s crust that have filled with fresh water. Rain , melting snow and water from water. Rain , melting snow and water from springs and rivers fill these depressions.springs and rivers fill these depressions.

A lake is sometimes formed when there is a A lake is sometimes formed when there is a natural blockage of a river or stream.natural blockage of a river or stream.

Lakes are usually found at high altitudes Lakes are usually found at high altitudes where glaciers were once present.where glaciers were once present.

PondsPonds

Ponds are shallow depression in the Earth’s Ponds are shallow depression in the Earth’s crust that have filled with fresh water.crust that have filled with fresh water.

They are smaller and not as deep as lakes.They are smaller and not as deep as lakes. Sunlight penetrates to the bottom of a pond Sunlight penetrates to the bottom of a pond

so plants can be found throughout a pond.so plants can be found throughout a pond.

ReservoirsReservoirs

The most frequent source of fresh water are The most frequent source of fresh water are artificial lakes known as reservoirs.artificial lakes known as reservoirs.

A reservoir is built by damming a stream or A reservoir is built by damming a stream or river that runs through a low lying area.river that runs through a low lying area.

Reservoirs help control flooding and store Reservoirs help control flooding and store water.water.

They sometimes provide irrigation for crops.They sometimes provide irrigation for crops. They can also be used to generate They can also be used to generate

electricity.electricity.

GroundwaterGroundwater

There is more fresh water below the surface There is more fresh water below the surface of the land than in all the lakes and of the land than in all the lakes and reservoirs on the Earth’s surface.reservoirs on the Earth’s surface.

Ground water moves slowly downward Ground water moves slowly downward through pores in the rocks and soil.through pores in the rocks and soil.

Material through which water can move Material through which water can move quickly is described as permeable.quickly is described as permeable.

Water cannot move quickly through Water cannot move quickly through impermeable material.impermeable material.

Zone of SaturationZone of Saturation

Groundwater continues to move downward Groundwater continues to move downward through permeable rock and soil until it through permeable rock and soil until it reaches an impermeable layer. This reaches an impermeable layer. This underground zone in which all the pores are underground zone in which all the pores are filled with water is called the zone of filled with water is called the zone of saturation.saturation.

Zone of AerationZone of Aeration

Above the water-filled zone, the ground is Above the water-filled zone, the ground is not as wet. Pores in the soil and rocks are not as wet. Pores in the soil and rocks are filled mostly with air. This drier region in filled mostly with air. This drier region in which the pores are filled mostly with air is which the pores are filled mostly with air is call the zone of aeration.call the zone of aeration.

Water TableWater Table

The surface between the zone of saturation The surface between the zone of saturation and the zone of aeration is an important and the zone of aeration is an important boundary. It marks the level below which boundary. It marks the level below which the ground is saturated, or soaked, with the ground is saturated, or soaked, with water. This level is called the water tablewater. This level is called the water table

Depth of the Water TableDepth of the Water Table

The depth of the water table varies based The depth of the water table varies based on location, climate, weather and man-made on location, climate, weather and man-made structures.structures.

Water Table LocationWater Table Location

In general, the water table is not very deep In general, the water table is not very deep near large bodies of water. near large bodies of water.

In high areas nears hills or mountains, the In high areas nears hills or mountains, the water table may be deep within the ground.water table may be deep within the ground.

In low-lying areas such as valleys with In low-lying areas such as valleys with swamps and marshes, the water table may swamps and marshes, the water table may be close to the surface.be close to the surface.

Water Table and ClimateWater Table and Climate

The depth of the water table varies with the The depth of the water table varies with the climate of an area.climate of an area.

It will be deep in dry areas such as deserts.It will be deep in dry areas such as deserts. It will be near the surface in low-lying forest It will be near the surface in low-lying forest

areas.areas. In very moist climates, the water table may In very moist climates, the water table may

come right to the surface and form a come right to the surface and form a swamp, lake or spring.swamp, lake or spring.

Water Table and WeatherWater Table and Weather

Even in the same area, the water table may Even in the same area, the water table may change.change.

Heavy rains and snow may make the water Heavy rains and snow may make the water table rise.table rise.

If there is a long dry period, the water table If there is a long dry period, the water table will fall.will fall.

Water Table and ManWater Table and Man

The depth of the water table will also The depth of the water table will also change if wells are overused or if many change if wells are overused or if many wells are located in a small area. Wells are wells are located in a small area. Wells are holes drilled to bring the water table to bring holes drilled to bring the water table to bring water to the surface.water to the surface.

Problems with Water TableProblems with Water Table

In areas where the water table is high, it In areas where the water table is high, it may flood foundations for buildings.may flood foundations for buildings.

It is easier and less expensive to dig wells in It is easier and less expensive to dig wells in areas where the water table is high.areas where the water table is high.

AquifersAquifers

As groundwater moves through a permeable As groundwater moves through a permeable rock layer, it often reaches an impermeable rock layer, it often reaches an impermeable rock layer or the water table. At this point, rock layer or the water table. At this point, the groundwater may move sideways the groundwater may move sideways through a layer of rock or sediment that through a layer of rock or sediment that allows it to pass freely. Such a layer is allows it to pass freely. Such a layer is called aquifer. Aquifers are usually layers of called aquifer. Aquifers are usually layers of sandstone, gravel, sand or cracked sandstone, gravel, sand or cracked limestone.limestone.

AquifersAquifers

Because rocks form in layers, sometimes a Because rocks form in layers, sometimes a layer of permeable rock may become layer of permeable rock may become trapped between two layer of impermeable trapped between two layer of impermeable rock. Sandstone trapped between two rock. Sandstone trapped between two layers of shale is an example.layers of shale is an example.

An aquifer is a source of groundwater that is An aquifer is a source of groundwater that is very vulnerable to pollution.very vulnerable to pollution.

Artesian WellsArtesian Wells

In some places where the underground rock In some places where the underground rock layers slope, an aquifer carries water from a layers slope, an aquifer carries water from a higher altitude to a lower altitude. If the higher altitude to a lower altitude. If the aquifer is trapped between two layers of aquifer is trapped between two layers of impermeable rock, pressure may build up at impermeable rock, pressure may build up at the lower altitude. A well drilled in to the the lower altitude. A well drilled in to the aquifer at this point will provide water aquifer at this point will provide water without pumping. It is called an artesian without pumping. It is called an artesian well.well.

CavernsCaverns

In some areas, the underlying rock is In some areas, the underlying rock is limestone. As groundwater moves down limestone. As groundwater moves down through the soil, it combines with carbon through the soil, it combines with carbon dioxide to form carbonic acid that can dioxide to form carbonic acid that can dissolve limestone. When water enters the dissolve limestone. When water enters the cracks in limestone, the carbonic acid cracks in limestone, the carbonic acid causes the cracks to become wider until causes the cracks to become wider until large underground caverns with passage large underground caverns with passage are formed.are formed.

Stalactites and StalagmitesStalactites and Stalagmites

These underground caverns have long These underground caverns have long stone icicles hanging from the ceiling stone icicles hanging from the ceiling (stalactites) and built up from the floors (stalactites) and built up from the floors (stalagmites.)(stalagmites.)

Stalactites and stalagmites are formed when Stalactites and stalagmites are formed when dissolved substances in groundwater are dissolved substances in groundwater are deposited.deposited.

Composition of WaterComposition of Water

A water molecule is the smallest particle that A water molecule is the smallest particle that has all the properties of water. has all the properties of water.

A water molecule forms when two atoms of A water molecule forms when two atoms of hydrogen and one of oxygen combine.hydrogen and one of oxygen combine.

In a water molecule the atom of oxygen has In a water molecule the atom of oxygen has a slight negative charge. Each atom of a slight negative charge. Each atom of hydrogen has a slight positive charge.hydrogen has a slight positive charge.

These charged ends give a water molecule These charged ends give a water molecule the property known as polarity.the property known as polarity.

Water as a SolventWater as a Solvent

It is the property of polarity that gives water It is the property of polarity that gives water molecules that makes water solvent.molecules that makes water solvent.

A solvent is a substance in which another A solvent is a substance in which another substance dissolves. The dissolving substance dissolves. The dissolving process produces a solution.process produces a solution.

A solution contains two or more substances A solution contains two or more substances mixed on the molecular level.mixed on the molecular level.

Water is known as the universal solvent.Water is known as the universal solvent.

Hardness of WaterHardness of Water

The taste, odor and appearance of water The taste, odor and appearance of water varies from area to areas. The differences varies from area to areas. The differences depend on the amounts and types of depend on the amounts and types of materials dissolved in the water.materials dissolved in the water.

Hard water contains larges amount of Hard water contains larges amount of dissolved minerals, especially calcium and dissolved minerals, especially calcium and magnesium.magnesium.

Soft water does not contain these minerals.Soft water does not contain these minerals.

Soft WaterSoft Water

Some water is softened naturally as it Some water is softened naturally as it passes through and reacts with rock passes through and reacts with rock formations that contain certain minerals. formations that contain certain minerals.

These minerals remove the calcium and These minerals remove the calcium and magnesium from the water, making it soft.magnesium from the water, making it soft.

Quality of WaterQuality of Water

Water is necessary to all life on Earth. It is Water is necessary to all life on Earth. It is therefore necessary to maintain the quality therefore necessary to maintain the quality of our water.of our water.

In nature, water is usually filtered as it In nature, water is usually filtered as it passes through sand and soil. Because so passes through sand and soil. Because so many different substances can dissolve in many different substances can dissolve in water, it is becoming more and more water, it is becoming more and more polluted. polluted.

Pollution of WaterPollution of Water

Water pollution limits the amounts and kinds Water pollution limits the amounts and kinds of wild life that can live in water. It also of wild life that can live in water. It also affects drinking water supplies. It destroys affects drinking water supplies. It destroys recreational areas. Nitrates and phosphates recreational areas. Nitrates and phosphates from fertilizers pollute groundwater. They from fertilizers pollute groundwater. They must be removed before the water can be must be removed before the water can be used for drinking or swimming.used for drinking or swimming.

Federal laws prevent industries from Federal laws prevent industries from dumping certain chemicals wastes.dumping certain chemicals wastes.