WATER

Grade 12 Environmental Science

Unit Overview Questions

Why is water so important, how much freshwater is

available to us, and how much of it are we using?

What causes freshwater shortages, and what can

be done about this problem?

What are the advantages and disadvantages of

withdrawing groundwater?

What are the advantages and disadvantages of

using dams and reservoirs to supply more water?

Unit Overview Questions (cont’d)

What are the advantages and disadvantages of transferring large amounts of water from one place to another?

Can removing salt from seawater solve our water supply problems?

How can we waste less water?

How can we use the earth’s water more sustainably?

What causes flooding, and what can we do about it?

Case Study: Water Conflicts in the

Middle East - A Preview of the Future

Many countries in the

Middle East, which has

one of the world’s

highest population

growth rates, face

water shortages.

Figure 14-1

Water Conflicts in the Middle East: A

Preview of the Future

Most water in this dry region comes from the Nile,

Jordan or Tigris rivers.

Countries are in disagreement as to who has water

rights.

Currently, there are no cooperative agreements for use

of 158 of the world’s 263 water basins that are

shared by two or more countries.

WATER’S IMPORTANCE, AVAILABILITY,

AND RENEWAL

Water keeps us alive, moderates climate, sculpts the

land, removes and dilutes wastes and pollutants, and

moves continually through the hydrologic cycle.

Only about 0.02% of the earth’s water supply is

available to us as liquid freshwater.

WATER’S IMPORTANCE, AVAILABILITY,

AND RENEWAL

Comparison of population

sizes and shares of the

world’s freshwater among

the continents.

Figure 14-2

Fig. 14-2, p. 307

Continent Percent of world's water resources

and population

Asia 60.5%

36%

Africa 10%

8% Europe

North and Central

America 7.3%

South America and

Caribbean 6.4%

26%

15%

5% Oceania

11.3%

0.5%

14%

WATER’S IMPORTANCE, AVAILABILITY,

AND RENEWAL

Some precipitation infiltrates the ground and is stored in

soil and rock (groundwater).

Water that does not sink into the ground or evaporate

into the air runs off (surface runoff) into bodies of

water.

The land from which the surface water drains into a body of

water is called its watershed or drainage basin.

Fig. 14-3, p. 308

Unconfined Aquifer Recharge Area

Precipitation Evaporation and transpiration Evaporation

Confined

Recharge

Area

Runoff

Flowing

artesian

well

Recharge

Unconfined

Aquifer

Stream Well

requiring a

pump Infiltration Water

table Lake Infiltration

WATER’S IMPORTANCE, AVAILABILITY,

AND RENEWAL

We currently use more than half of the world’s reliable

runoff of surface water and could be using 70-90% by

2025.

About 70% of the water we withdraw from rivers,

lakes, and aquifers is not returned to these sources.

Irrigation is the biggest user of water (70%), followed

by industries (20%) and cities and residences (10%).

TOO LITTLE FRESHWATER

About 41% of the world’s population lives in river

basins that do not have enough freshwater.

Many parts of the world are experiencing:

Rivers running dry.

Lakes and seas shrinking.

Falling water tables from overpumped aquifers.

Stress on the World’s River Basins

Comparison of the amount of water available with the

amount used by humans.

Figure 14-6

Fig. 14-6, p. 311

Europe

North

America Asia

Africa

South

America Australia

Stress

High None

Case Study: Who Should Own and

Manage Freshwater Resources

There is controversy over whether water supplies should

be owned and managed by governments or by private

corporations.

European-based water companies aim to control 70%

of the U.S. water supply by buying up water companies

and entering into agreements with cities to manage

water supplies.

How Would You Vote?

Should private companies own or manage most of the world's water resources? a. No. Democratically elected governments, which are

accountable to the voters, should own and manage water resources.

b. Qualified yes. Governments should own the water, but expert private companies should manage it.

c. Depends. Each case must be decided independently. The record on private versus public ownership is mixed.

d. Yes. Private companies have more expertise and experience in managing water resources than most government bureaucrats.

TOO LITTLE FRESHWATER

Cities are outbidding farmers for water supplies

from rivers and aquifers.

Countries are importing grain as a way to reduce

their water use.

More crops are being used to produce biofuels.

Our water options are:

Get more water from aquifers and rivers, desalinate

ocean water, waste less water.

WITHDRAWING GROUNDWATER TO

INCREASE SUPPLIES

Most aquifers are renewable resources unless water is

removed faster than it is replenished or if they are

contaminated.

Groundwater depletion is a growing problem mostly

from irrigation.

At least one-fourth of the farms in India are being irrigated

from overpumped aquifers.

Fig. 14-7, p. 313

Trade-Offs

Withdrawing Groundwater

Advantages Disadvantages

Useful for drinking

and irrigation

Aquifer depletion from

overpumping

Available year-

round

Sinking of land

(subsidence) from

overpumping

Exists almost

everywhere Polluted aquifers for

decades or centuries

Renewable if not

overpumped or

contaminated

Saltwater intrusion into

drinking water supplies

near coastal areas

Reduced water flows

into surface waters No evaporation

losses

Cheaper to extract

than most surface

waters

Increased cost and

contamination from

deeper wells

Groundwater Depletion:

A Growing Problem

The Ogallala, the world’s largest aquifer, is most of the

red area in the center (Midwest).

Areas of greatest aquifer depletion from groundwater overdraft in the continental U.S.

Figure 14-8

Other Effects of Groundwater

Overpumping

Groundwater

overpumping can

cause land to sink,

and contaminate

freshwater

aquifers near

coastal areas with

saltwater.

Figure 14-11

Other Effects of Groundwater

Overpumping

Sinkholes form when the

roof of an underground

cavern collapses after

being drained of

groundwater.

Figure 14-10

Groundwater Pumping in Saudi Arabia

(1986 – 2004)

Irrigation systems from the nonrenewable aquifer appear as green dots. Brown dots are wells that have gone dry.

Figure 14-9

Fig. 14-12, p. 316

Solutions

Groundwater Depletion

Prevention Control

Waste less water Raise price of water

to discourage waste

Subsidize water

conservation

Ban new wells in

aquifers near

surface waters

Tax water pumped

from wells near

surface waters

Buy and retire

groundwater

withdrawal rights

in critical areas

Do not grow water-

intensive crops in

dry areas

Set and enforce

minimum stream

flow levels

USING DAMS AND RESERVOIRS TO

SUPPLY MORE WATER

Large dams and reservoirs can produce cheap

electricity, reduce downstream flooding, and provide

year-round water for irrigating cropland, but they also

displace people and disrupt aquatic systems.

Fig. 14-13a, p. 317

Provides water for year-round irrigation of cropland

Flooded land destroys forests or cropland and displaces people

Large losses of water through evaporation

Provides water for drinking Downstream

cropland and estuaries are deprived of nutrient-rich silt

Reservoir is useful for recreation and fishing

Risk of failure and devastating downstream flooding

Can produce cheap electricity (hydropower)

Downstream flooding is reduced

Migration and spawning of some fish are disrupted

Fig. 14-13b, p. 317

Powerlines

Reservoir

Dam

Powerhouse Intake

Turbine

Case Study: The Colorado Basin –

an Overtapped Resource

The Colorado River has so many dams and

withdrawals that it often does not reach the ocean.

14 major dams and reservoirs, and canals.

Water is mostly used in desert area of the U.S.

Provides electricity from hydroelectric plants for 30 million

people (1/10th of the U.S. population).

Case Study: The Colorado Basin –

an Overtapped Resource

Lake Powell, is the second largest reservoir in the U.S.

It hosts one of the hydroelectric plants located on the Colorado River.

Figure 14-15

The Colorado River Basin

Figure 14-14

How Would You Vote?

Do the advantages of large dams outweigh their disadvantages?

a. No. Large dams inflict extensive environmental damage and humans must learn to meet their needs without them.

b. Yes. Dams are critical in providing water and electricity for people, especially in developing countries.

Case Study:

China’s Three Gorges Dam

There is a debate over whether the advantages of the world’s largest dam and reservoir will outweigh its disadvantages.

The dam will be 2 kilometers long.

The electric output will be that of 18 large coal-burning or nuclear power plants.

It will facilitate ship travel reducing transportation costs.

Dam will displace 1.2 million people.

Dam is built over seismatic fault and already has small cracks.

Dam Removal

Some dams are being removed for ecological

reasons and because they have outlived their

usefulness.

In 1998 the U.S. Army Corps of Engineers announced

that it would no longer build large dams and diversion

projects in the U.S.

The Federal Energy Regulatory Commission has

approved the removal of nearly 500 dams.

Removing dams can reestablish ecosystems, but can also

re-release toxicants into the environment.

TRANSFERRING WATER FROM ONE

PLACE TO ANOTHER

Transferring water can make unproductive areas more

productive but can cause environmental harm.

Promotes investment, jobs and strong economy.

It encourages unsustainable use of water in areas water is

not naturally supplied.

Case Study: The California Experience

A massive transfer of

water from water-rich

northern California to

water-poor southern

California is

controversial.

Figure 14-16

Fig. 14-16, p. 321

CALIFORNIA

Sacramento

River

North Bay

Aqueduct Lake Tahoe

San Francisco Sacramento

South Bay

Aqueduct

Hoover Dam and

Reservoir (Lake

Mead)

NEVADA

UTAH

Fresno

San Luis Dam

and Reservoir Los Angeles

Aqueduct

Colorado

River

California Aqueduct

Santa Barbara

Colorado River

Aqueduct Central Arizona

Project

ARIZONA

Los Angeles

Salton Sea Phoenix San Diego

Tucson

MEXICO

Feather

River

Shasta Lake

Oroville Dam and

Reservoir

Case Study: The Aral Sea Disaster

The Aral Sea was once the world’s fourth largest

freshwater lake.

Figure 14-17

Case Study: The Aral Sea Disaster

Diverting water from the Aral Sea and its two feeder

rivers mostly for irrigation has created a major

ecological, economic, and health disaster.

About 85% of the wetlands have been eliminated and

roughly 50% of the local bird and mammal species have

disappeared.

Since 1961, the sea’s salinity has tripled and the water has

dropped by 22 meters most likely causing 20 of the 24

native fish species to go extinct.

DESALTING SEAWATER, SEEDING CLOUDS, AND

TOWING ICEBERGS AND GIANT BAGGIES

Removing salt from seawater by current methods is

expensive and produces large amounts of salty

wastewater that must be disposed of safely.

Distillation: heating saltwater until it evaporates, leaves

behind water in solid form.

Reverse osmosis: uses high pressure to force saltwater

through a membrane filter.

Seeding clouds with tiny particles of chemicals to

increase rainfall towing icebergs or huge bags filled

with freshwater to dry coastal areas have all been

proposed but are unlikely to provide significant amounts

of freshwater.

DESALTING SEAWATER, SEEDING CLOUDS, AND

TOWING ICEBERGS AND GIANT BAGGIES

INCREASING WATER SUPPLIES BY

WASTING LESS WATER

We waste about two-thirds of the water we use, but we

could cut this waste to 15%.

65-70% of the water people use throughout the world is

lost through evaporation, leaks, and other losses.

Water is underpriced through government subsidies.

The lack of government subsidies for improving the

efficiency of water use contributes to water waste.

How Would You Vote?

Should water prices be raised sharply to help

reduce water waste?

a. No. Poor people, farmers, ranchers, and small

businesses would suffer from price increases.

b. Yes. People would be more likely to conserve water

if it is more expensive.

INCREASING WATER SUPPLIES BY

WASTING LESS WATER

Sixty percent of the world’s irrigation water is currently

wasted, but improved irrigation techniques could cut this

waste to 5-20%.

Center-pivot, low pressure sprinklers sprays water

directly onto crop.

It allows 80% of water to reach crop.

Has reduced depletion of Ogallala aquifer in Texas High

Plains by 30%.

Fig. 14-18, p. 325

Center pivot

Drip irrigation

Gravity flow

(efficiency 60% and

80% with surge

valves)

Above- or below-

ground pipes or tubes

deliver water to

individual plant roots.

Water usually comes from

an aqueduct system or a

nearby river.

(efficiency 90–95%)

(efficiency 80%–95%)

Water usually pumped

from underground and

sprayed from mobile

boom with sprinklers.

Fig. 14-19, p. 326

Solutions

Reducing Irrigation Water Waste

• Line canals bringing water to irrigation ditches

• Level fields with lasers

• Irrigate at night to reduce evaporation

• Monitor soil moisture to add water only

when necessary

• Polyculture

• Organic farming

• Don't grow water-thirsty crops in dry areas

• Grow water-efficient crops using drought

resistant and salt-tolerant crop varieties

• Irrigate with treated urban waste water

• Import water-intensive crops and meat

Solutions: Getting More Water for Irrigation in

Developing Countries – The Low-Tech Approach

Many poor farmers in

developing countries use

low-tech methods to pump

groundwater and make

more efficient use of

rainfall.

Figure 14-20

Fig. 14-21, p. 327

Solutions

Reducing Water Waste

• Redesign manufacturing processes

• Repair leaking underground pipes

• Landscape yards with plants that

require little water

• Use drip irrigation

• Fix water leaks

• Use water meters

• Raise water prices

• Use waterless composting toilets

• Require water conservation in water-

short cities

• Use water-saving toilets, showerheads,

and front loading clothes washers

• Collect and reuse household water to

irrigate lawns and nonedible plants

• Purify and reuse water for houses,

apartments, and office buildings

• Don't waste energy

Raising the Price of Water:

A Key to Water Conservation

We can reduce water use and waste by raising the

price of water while providing low lifeline rates for the

poor.

When Boulder, Colorado introduced water meters, water

use per person dropped by 40%.

A 10% increase in water prices cuts domestic water use by

3-7%.

Solutions: Using Less Water to Remove

Industrial and Household Wastes

We can mimic the way nature deals with wastes instead

of using large amounts of high-quality water to wash

away and dilute industrial and animal wastes.

Use nutrients in wastewater before treatment as soil

fertilizer.

Use waterless and odorless composting toilets that convert

human fecal matter into a small amount of soil material.

TOO MUCH WATER

Heavy rainfall, rapid snowmelt, removal of vegetation,

and destruction of wetlands cause flooding.

Floodplains, which usually include highly productive

wetlands, help provide natural flood and erosion

control, maintain high water quality, and recharge

groundwater.

To minimize floods, rivers have been narrowed with

levees and walls, and dammed to store water.

TOO MUCH WATER

Comparison of St. Louis, Missouri under normal conditions (1988) and after severe flooding (1993).

Figure 14-22

TOO MUCH WATER

Human activities have contributed to flood deaths and

damages.

Figure 14-23

Fig. 14-23a, p. 330

Oxygen

released by

vegetation

Diverse

ecological

habitat

Evapotranspiration

Trees reduce soil

erosion from heavy

rain and wind

Agricultural

land Steady

river flow

Leaf litter

improves soil

fertility

Tree roots stabilize

soil and aid water

flow

Vegetation releases

water slowly and

reduces flooding

Forested Hillside

Fig. 14-23b, p. 330

Tree plantation

Roads

destabilize

hillsides

Evapotranspiration decreases

Ranching accelerates

soil erosion by water

and wind

Winds remove fragile

topsoil

Agricultural land is

flooded and silted up

Gullies and

landslides

Heavy rain leaches

nutrients from soil and

erodes topsoil

Silt from erosion blocks rivers and reservoirs

and causes flooding downstream

Rapid runoff

causes flooding

After Deforestation

Fig. 14-24, p. 331

Solutions

Reducing Flood Damage

Prevention Control

Preserve forests on

watersheds

Strengthen and

deepen streams

(channelization)

Preserve and

restore wetlands

in floodplains

Tax all development

on floodplains

Build levees or

floodwalls along

streams

Use floodplains

primarily for

recharging aquifers,

sustainable

agriculture and

forestry, and

recreation

Build dams

SOLUTIONS: USING WATER

MORE SUSTAINABLY

We can use water more

sustainably by cutting waste,

raising water prices,

preserving forests and

wetlands in water basins, and

slowing population growth.

Figure 14-25

Fig. 14-25, p. 333

What Can You Do?

Water Use and Waste

• Use water-saving toilets, showerheads, and faucet aerators.

• Shower instead of taking baths, and take short showers.

• Stop water leaks.

• Turn off sink faucets while brushing teeth, shaving, or washing.

• Flush toilets only when necessary.

• Wash only full loads of clothes or use the lowest water-level for

smaller loads.

• Use recycled (gray) water for lawn, gardens, house plants,

car washing.

• Wash a car from a bucket of soapy water, and use the hose for

rinsing only.

• If you use a commercial car wash, try to find one that recycles its

water.

• Replace your lawn with native plants that need little if any watering

and decorative gravel or rocks.

• Water lawns and gardens in the early morning or evening.

• Sweep or blow off driveways instead of hosing off with water.

• Use drip irrigation and mulch for gardens and flowerbeds.