Download LT 6E Active Practice Key Explain why access to water is a health

LT 6E Active Practice Key
1. Explain why access to water is a health issue, an economic issue, a women’s and children’s issue, a
national and global security issue, and an environmental issue. What percentage of the earth’s
freshwater is available to us?
 Access to water is a global health issue because an average of 3,900 children younger than age
5 die from waterborne infectious diseases because they do not have access to safe drinking
water. It is an economic issue because it is vital for reducing poverty and producing food and
energy. It is an issue for women and children in less-developed countries because almost half
of the world’s people do not have water piped to their homes and women generally bear the
burden of accessing water. It is also a national and global security issue because of increasing
tensions both within and between nations over access to limited water resources. It is also an
environmental issue because excessive withdrawal of water from rivers and aquifers results
in falling water tables, decreasing river flows, shrinking lakes, and disappearing wetlands.
 Only about 0.024% of the world’s freshwater is available to us.
2. Define groundwater, zone of saturation, water table, and aquifer. Distinguish among surface
water, surface runoff, and reliable surface runoff.
 Some precipitation infiltrates the ground and percolates downward through spaces in soil,
gravel, and rock until an impenetrable layer of rock stops it. The water in these spaces is
called groundwater.
 The spaces in soil and rock close to the earth’s surface hold little moisture. Below a certain
depth, in the zone of saturation, these spaces are completely filled with water.
 The top of this groundwater zone is the water table. It falls in dry weather, or when we
remove groundwater faster than nature can replenish it, and it rises in wet weather.
 Deeper down are geological layers called aquifers: underground caverns and porous layers of
sand, gravel, or bedrock through which groundwater flows.
 Surface water is the freshwater from precipitation and snowmelt that flows across the earth’s
land surface and into lakes, wetlands, streams, rivers, estuaries, and ultimately to the oceans.
 Precipitation that does not infiltrate the ground or return to the atmosphere by evaporation is
called surface runoff.
 Two-thirds of the annual surface runoff in rivers and streams is lost by seasonal floods and is
not available for human use. The remaining one-third is reliable surface runoff, which we can
generally count on as a source of freshwater from year to year.
3. Define and give an example of a water footprint. What is virtual water?
 A water footprint is a rough measure of the volume of water that we use directly and
indirectly to keep ourselves alive and to support our lifestyles. An example would all of the
water each of us use directly and indirectly.
 Virtual water is Water that is not directly consumed but is used to produce food and other
products.
4. What are the advantages and disadvantages of withdrawing groundwater?
 Advantages of withdrawing groundwater include:
o Useful for drinking and irrigation.
o Available year-round.
o Exists almost everywhere.
o Renewable if not overpumped or contaminated.
o No evaporation losses.
o Cheaper to extract than most surface waters.
5. What is a dam? What is a reservoir? What are the advantages and disadvantages of using large
dams and reservoirs?
 Large dams are structures built across rivers to block some of the flow of water.
 Reservoirs store water collected behind the dams.
 Trade-offs: advantages and disadvantages of large dams and reservoirs. Dams and reservoirs
capture and store runoff and release it as needed to control floods, generate electricity, and
supply water for irrigation and for towns and cities. Reservoirs also provide recreational
activities such as swimming, fishing, and boating. Worldwide, dams have displaced 40– 80
million people from their homes. Dams have flooded an area of mostly productive land
roughly equal to the area of the U. S. state of California, and it has impaired some of the
important ecological services rivers provide. And according to the 2007 WWF study, about
one- fifth of the world’s freshwater fish and plant species are either extinct or endangered
primarily because dams and water withdrawals have destroyed many free- flowing rivers.
 Rivers deliver nutrients to sea to help sustain coastal fisheries, deposit silt that maintains
deltas, purify water, renew and renourish wetlands and provide habitats for wildlife.
6. Describe the California Water Project and the controversy over this water transfer project.
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One of the world’s largest water transfer projects is the California Water Project.. It uses giant
dams, pumps, and aqueducts to transport water from water rich northern California to waterpoor southern California’s heavily populated agricultural regions and cities. This project
supplies massive amounts of water to areas that, without such water transfers, would be
water should be allocated under this project. Southern Californians want more water to grow
more crops and to support growing urban areas. Northern Californians counter that sending
more water south degrades the Sacramento River, threatens fisheries, and reduces the river’s
power to flush pollutants out of San Francisco Bay. They point to studies showing that making
irrigation just 10% more efficient would provide enough water for domestic and industrial
uses in southern California. But low water prices, mostly because government subsidies make
it uneconomical for farmers to invest in improving irrigation efficiency.
7. Define desalination and distinguish between distillation and reverse osmosis as methods for
desalinating water. What are three major limitations on the widespread use of desalination?
 Desalination involves removing dissolved salts from ocean water or from brackish water for
domestic use. The two most widely used methods are distillation and reverse osmosis.
Distillation involves heating saltwater until it evaporates (leaving behind salts in solid form)
and condenses as freshwater. Reverse osmosis (or microfiltration) uses high pressure to force
saltwater through a membrane filter with pores small enough to remove the salt.
 There are three major problems with the widespread use of desalination.
o Desalination is expensive, because it takes a lot of energy to desalinate water. Pumping
desalinated water inland also takes a lot of energy and is costly.
o Pumping large volumes of seawater through pipes and using chemicals to sterilize the
water and keep down algae growth kills many marine organisms and also requires large
inputs of energy to run the pumps.
o Desalination produces huge quantities of salty wastewater that must go somewhere.