Environmental Engineering Reference
In-Depth Information
Our liquid planet glows like a soft blue sapphire in the hard-
edged darkness of space. There is nothing else like it in the so-
lar system. It is because of water.
J
OHN
T
ODD
11-1 WATER'S IMPORTANCE, USE,
AND RENEWAL
Science: Importantance and Availability
of Fresh Water
Water keeps us alive, moderates climate, sculpts the
land, removes and dilutes wastes and pollutants, and
is recycled by the hydrologic cycle.
We live on the water planet, with a precious film of wa-
ter—most of it salt water—covering about 71% of the
earth's surface. All organisms are made up of mostly
water. Look in the mirror. What you see is about 60%
water, most of it inside your cells.
You could survive for several weeks without food
but only a few days without water. It takes huge
amounts of water to supply you with food, provide
shelter, and meet your other needs and wants. Water
also plays a key role in sculpting the earth's surface,
moderating climate, and removing and diluting water-
soluble wastes and pollutants.
Despite its importance, water is one of our most
poorly managed resources. We waste it and pollute it.
We also charge too little for making it available. This
encourages still greater waste and pollution of this re-
newable resource, for which we have no substitute.
As Benjamin Franklin said many decades ago, “It is
not until the well runs dry that we know the worth of
water.”
Only a tiny fraction of the planet's abundant wa-
ter supply is readily available to us as fresh water
(Figure 11-2, p. 238). If the world's water supply
amounted to only 100 liters (26 gallons), our usable
supply of fresh water would be only about 0.014 liter,
or 2.5 teaspoons!
Fortunately, the world's freshwater supply is con-
tinuously collected, purified, recycled, and distributed
in the solar-powered
hydrologic cycle
(Figure 3-24,
p. 54). This magnificent water recycling and purifica-
tion system works well as long as we do not overload
water systems with slowly degradable and nondegrad-
able wastes or withdraw water from underground sup-
plies faster than it is replenished. In parts of the world,
we are doing both of these things.
Differences in average annual precipitation divide
the world's countries and people into water
haves
and
have-nots.
Some places get lots of rain (the dark and
light green areas in Figure 5-2, p. 80), whereas others
get very little (the yellow-green areas in Figure 5-2).
For example, Canada, with only 0.5% of the world's
population, has one-fifth of the world's fresh water.
China, with one-fifth of the world's people, has only
7% of the supply.
This chapter discusses the water supply and pollution
problems we face and ways to use water—an irre-
placeable resource—more sustainably. It addresses the
following questions:
Why is water so important, how much fresh
water is available to us, and how much of it are
we using?
■
What causes freshwater shortages, and what can
we do about these problems?
■
What causes flooding, and what can we do
about it?
■
What pollutes water, where do these pollutants
come from, and what effects do they have?
■
What are the major water pollution problems af-
fecting streams, lakes, and groundwater?
■
What are the major water pollution problems af-
fecting oceans?
■
How can we prevent and reduce water pollution?
■
How can we use the earth's water more
sustainably?
■
KEY IDEAS
■
We currently use more than half of the world's reli-
able runoff of surface water and could be using
70-90% by 2025.
■
One of every six people does not have regular ac-
cess to an adequate, safe, and affordable supply of
clean water, and this number could increase to at
least one of every four people by 2050.
■
We can use water more sustainably by cutting
waste, raising water prices, preserving forests in water
basins, and slowing population growth.
■
Stream pollution in most developing countries is a
serious and growing problem.
■
Groundwater pollution is a serious and growing
problem in parts of the world.
■
We can reduce pollution of coastal waters near
heavily populated areas by preventing or reducing
the flow of pollution from the land and from streams
emptying into the ocean.
