The Water Pollution Crisis

The Module 7.3 described one aspect of the global water crisis, the water shortages that
afflict many arid and densely populated areas. The global water crisis also involves
water pollution, because to be useful for drinking and irrigation, water must not be
polluted beyond certain thresholds. According to the World Health Organization, in
2008 approximately 880 million people in the world (or 13% of world population) did not
have access to improved (safe) drinking water (World Health Statistics, 2010) (See
Figure 7.14.17.14.1). At the same time, about 2.6 billion people (or 40% of world
population) lived without improved sanitation (see Figure 7.14.27.14.2), which is
defined as having access to a public sewage system, septic tank, or even a simple pit
latrine. Each year approximately 1.7 million people die from diarrheal diseases
associated with unsafe drinking water, inadequate sanitation, and poor hygiene, e.g.,
hand washing with soap. Almost all of these deaths are in developing countries, and
around 90% of them occur among children under the age of 5 (see Figure 7.14.37.14.3).
Compounding the water crisis is the issue of social justice; poor people more
commonly lack clean water and sanitation than wealthy people in similar areas.
Globally, improving water, sanitation, and hygiene could prevent up to 9% of all disease
and 6% of all deaths. In addition to the global waterborne disease crisis, chemical
pollution from agriculture, industry, cities, and mining threatens global water quality.
Some chemical pollutants have serious and well-known health effects; however, many
others have poorly known long-term health effects. In the U.S. currently more than
40,000 water bodies fit the definition of “impaired” set by EPA (See Figure 7.14.47.14.4),
which means they could neither support a healthy ecosystem nor meet water quality
standards. In Gallup public polls conducted over the past decade Americans
consistently put water pollution and water supply as the top environmental concerns
over issues such as air pollution, deforestation, species extinction, and global warming.
Figure 7.14.17.14.1 Proportion of Population by Country Using Improved Drinking Water
Sources in 2008. Improved drinking water sources, e.g., household connections, public
standpipes, boreholes, protected dug wells and springs, and rainwater collections, are
defined as those more likely to provide safe water than unimproved water sources, e.g.,
unprotected wells and springs, vendor-provided water, bottled water (unless water for
other uses is available from an improved source), and tanker truck-provided
water. Source: World Health
Organization

Figure 7.14.27.14.2 Proportion of Population by Country Using Improved Sanitation

Facilities in 2008. Improved sanitation facilities, e.g., connection to public sewers or
septic systems, pour-flush latrines, pit latrines, and ventilated improved pit latrines, are
defined as those more likely to be sanitary than unimproved facilities, e.g., bucket
latrines, public latrines, and open pit latrines. Source: World Health
Organization

Figure 7.14.37.14.3 Deaths by Country from Diarrhea Caused by Unsafe Water,

Unimproved Sanitation, and Poor Hygiene in Children Less than 5 Years Old,
2004. Source: World Health
Organization

Figure 7.14.47.14.4 Percentage of Impaired Water Bodies in a Watershed by State in

USA Based on US EPA Data in 2000. Map of watersheds containing impaired water
bodies from the U.S. Environmental Protection Agency's 1998 list of impaired
waters Source: U.S. Geological Survey

Water Chemistry Overview

Compared to other molecules of similar molecular weight, water (H2O) has unique
physical properties including high values for melting and boiling point, surface tension
(water’s cohesion, or “stickiness”), and capacity to dissolve soluble minerals, i.e., act
as a solvent. These properties are related to its asymmetrical structure and polar
nature, which means it is electrically neutral overall but it has a net positive charge on
the side with the two hydrogen atoms and a net negative charge on the oxygen side (see
Figure 7.14.57.14.5). This separation of the electrical charge within a water molecule
results in hydrogen bondswith other water molecules, mineral surfaces (hydrogen
bonding produces the water films on minerals in the unsaturated zone of the
subsurface), and dissolved ions (atoms with a negative or positive charge). Many
minerals and pollutants dissolve readily in water because water forms hydration
shells (spheres of loosely coordinated, oriented water molecules) around ions.

Figure 7.14.57.14.5 Structure of Water, Polar Charge of Water, and Hydrogen Bonds
between Water Molecules. Source: Michal Maňas at Wikimedia Commons

Any natural water contains dissolved chemicals; some of these are important human
nutrients, while others can be harmful to human health. The abundance of a water
pollutant is commonly given in very small concentration units such as parts per million
(ppm) or even parts per billion (ppb). An arsenic concentration of 1 ppm means 1 part of
arsenic per million parts of water. This is equivalent to one drop of arsenic in 50 liters of
water. To give you a different perspective on appreciating small concentration units,
converting 1 ppm to length units is 1 cm (0.4 in) in 10 km (6 miles) and converting 1 ppm
to time units is 30 seconds in a year. Total dissolved solids (TDS) represent the total
amount of dissolved material in water. Average TDS (salinity) values for rainwater, river
water, and seawater are about 4 ppm, 120 ppm, and 35,000 ppm. As discussed in
Module 5.2, the most important processes that affect the salinity of natural waters are
evaporation, which distills nearly pure water and leaves the dissolved ions in the
original water, and chemical weathering, which involves mineral dissolution that adds
dissolved ions to water. Fresh water is commonly defined as containing less than either
1,000 or 500 ppm TDS, but the US Environmental Protection Agency (EPA) recommends
that drinking water not exceed 500 ppm TDS or else it will have an unpleasant salty
taste.

Water Pollution Overview

Water pollution is the contamination of water by an excess amount of a substance that

can cause harm to human beings and the ecosystem. The level of water pollution
depends on the abundance of the pollutant, the ecological impact of the pollutant, and
the use of the water. Pollutants are derived from biological, chemical, or physical
processes. Although natural processes such as volcanic eruptions or evaporation
sometimes can cause water pollution, most pollution is derived from human, land-
based activities (see Figure 7.14.67.14.6). Water pollutants can move through different
water reservoirs, as the water carrying them progresses through stages of the water
cycle (see Figure 7.14.77.14.7). Water residence time (the average time that a water
molecule spends in a water reservoir) is very important to pollution problems because it
affects pollution potential. Water in rivers has a relatively short residence time, so
pollution usually is there only briefly. Of course, pollution in rivers may simply move to
another reservoir, such as the ocean, where it can cause further problems.
Groundwater is typically characterized by slow flow and longer residence time, which
can make groundwater pollution particularly problematic. Finally, pollution residence
time can be much greater than the water residence time because a pollutant may be
taken up for a long time within the ecosystem or absorbed onto sediment.
 Figure 7.14.6
7.14.6 Water Pollution. Obvious water pollution in the form of floating debris; invisible
water pollutants sometimes can be much more harmful than visible
ones. Source: Stephen Codrington at Wikimedia
Commons
Figure 7.14.77.14.7 Sources of Water Contamination. Sources of some water pollutants
and movement of pollutants into different water reservoirs of the water
cycle. Source: U.S. Geological Survey

Pollutants enter water supplies from point sources, which are readily identifiable and
relatively small locations, or nonpoint sources, which are large and more diffuse areas.
Point sources of pollution include animal “factory” farms that raise a large number and
high density of livestock such as cows, pigs, and chickens (see Figure 7.14.87.14.8) and
discharge pipes from a factories or sewage treatment plants. Combined sewer systems
that have a single set of underground pipes to collect both sewage and storm water
runoff from streets for wastewater treatment can be major point sources of pollutants.
During heavy rain, storm water runoff may exceed sewer capacity, causing it to back up
and spilling untreated sewage into surface waters (see Figure 7.14.97.14.9). Nonpoint
sources of pollution include agricultural fields, cities, and abandoned mines. Rainfall
runs over the land and through the ground, picking up pollutants such as herbicides,
pesticides, and fertilizer from agricultural fields and lawns; oil, antifreeze, car detergent,
animal waste, and road salt from urban areas; and acid and toxic elements from
abandoned mines. Then, this pollution is carried into surface water bodies and
groundwater. Nonpoint source pollution, which is the leading cause of water pollution in
the U.S., is usually much more difficult and expensive to control than point source
pollution because of its low concentration, multiple sources, and much greater volume
of water.
 Figure 7.14.87.14.8 A Commercial Meat Chicken Production House. This chicken
factory farm is a possible major point source of water pollution. Source: Larry Rana at
Wikimedia
Commons

Figure 7.14.97.14.9 Combined Sewer System. A combined sewer system is a possible

major point source of water pollution during heavy rain due to overflow of untreated
sewage. During dry weather (and small storms), all flows are handled by the publicly
owned treatment works (POTW). During large storms, the relief structure allows some of
the combined stormwater and sewage to be discharged untreated to an adjacent water
body. Source: U.S. Environmental Protection Agency at Wikimedia Commons

Types of Water Pollutants

Oxyden-demanding waste is an extremely important pollutant to ecosystems. Most

surface water in contact with the atmosphere has a small amount of dissolved oxygen,
which is needed by aquatic organisms for cellular respiration. Bacteria decompose
dead organic matter (chemically represented in a simplified way as CH2O) and remove
dissolved oxygen (O2) according to the following reaction:

CH2O+O2→CO2+H2OCH2O+O2→CO2+H2O

Too much decaying organic matter in water is a pollutant because it removes oxygen
from water, which can kill fish, shellfish, and aquatic insects. The amount of oxygen
used by aerobic (in the presence of oxygen) bacterial decomposition of organic matter
is called biochemical oxygen demand (BOD). The major source of dead organic matter
in most natural waters is sewage; grass and leaves are smaller sources. An unpolluted
water body with respect to oxygen is a turbulent river that flows through a natural forest.
Turbulence continually brings water in contact with the atmosphere where the
O2 content is restored. The dissolved oxygen content in such a river ranges from 10 to 14
ppm O2, BOD is low, and clean-water fish, e.g., bass, trout, and perch dominate. A
polluted water body with respect to oxygen is a stagnant deep lake in an urban setting
with a combined sewer system. This system favors a high input of dead organic carbon
from sewage overflows and limited chance for water circulation and contact with the
atmosphere. In such a lake, the dissolved O2 content is ≤5 ppm O2, BOD is high, and low
O2-tolerant fish, e.g., carp and catfish dominate.

Excessive plant nutrients, particularly nitrogen (N) and phosphorous (P), are pollutants
closely related to oxygen-demanding waste. Aquatic plants require about 15 nutrients
for growth, most of which are plentiful in water. N and P are called limiting nutrients,
because they usually are present in water at low concentrations and therefore restrict
the total amount of plant growth. This explains why N and P are major ingredients in
most fertilizer. High concentrations of N and P from human sources (mostly agricultural
and urban runoff including fertilizer, sewage, and P-based detergent) can cause cultural
eutrophication, which involves the rapid growth of aquatic plants, particularly algae,
called an algal bloom. Thick mats of floating and rooted green or sometimes red algae
(see Figure 7.14.107.14.10) create water pollution, damage the ecosystem by clogging
fish gills and blocking sunlight, and damage lake aesthetics by making recreation
difficult and creating an eyesore. A small percentage of algal species produce toxins
that can kill fish, mammals, and birds, and may cause human illness; explosive growths
of these algae are called harmful algal blooms (see Figure 7.14.117.14.11). When the
prolific algal layer dies, it becomes oxygen-demanding waste, which can create very low
O2 water (<~2 ppm O2), called hypoxia or dead zone because it causes death to
organisms that are unable to leave that environment. An estimated 50% of lakes in
North America, Europe, and Asia are negatively impacted by cultural eutrophication. In
addition, the size and number of marine hypoxic zones have grown dramatically over the
past 50 years (see Figure 7.14.127.14.12), including a very large dead zone located
offshore Louisiana in the Gulf of Mexico. Cultural eutrophication and hypoxia are
difficult to combat, because they are caused primarily by nonpoint source pollution,
which is difficult to regulate, and N and P, which are difficult to remove from wastewater.

Figure 7
.14.107.14.10 Algal Bloom in River in Sichuan, China. Algal blooms can present
problems for ecosystems and human society. Source: Felix Andrews via Wikimedia
Commons
Figure 7.14.117.14.11 Harmful Algal Bloom. Harmful algal bloom with deep red
color. Source: Kai Schumann via National Oceanic and Atmospheric
Administration

Figure 7.14.127.14.12 Aquatic Dead Zones. Zones of hypoxia shown as red circles.
Black dots show hypoxia zones of unknown size, brown shading shows population
density, and blue shading shows density of particulate organic carbon, an indicator of
organic productivity. Source: Robert Simmon & Jesse Allen at NASA Earth Observatory
via Wikimedia Commons

Pathogens are disease-causing microorganisms, e.g., viruses, bacteria, parasitic

worms, and protozoa, which cause a variety of intestinal diseases such as dysentery,
typhoid fever, hepatitis, and cholera. Pathogens are the major cause of the water
pollution crisis discussed at the beginning of this section. Unfortunately nearly a billion
people around the world are exposed to waterborne pathogen pollution daily and
around 1.5 million children mainly in underdeveloped countries die every year of
waterborne diseases from pathogens (see Figure 7.14.37.14.3). Pathogens enter water
primarily from human and animal fecal waste due to inadequate sewage treatment. In
many underdeveloped countries, sewage is discharged into local waters either
untreated or after only rudimentary treatment. In developed countries untreated
sewage discharge can occur from overflows of combined sewer systems, poorly
managed livestock factory farms, and leaky or broken sewage collection systems (see
Figure 7.14.147.14.14). Water with pathogens can be remediated by adding chlorine or
ozone, by boiling, or by treating the sewage in the first place.

Figure 7.
14.137.14.13 Overflowing Sanitary Sewer. A manhole cover blown off by a June 2006
sanitary sewer overflow in Rhode Island. Source: U.S. Environmental Protection
Agency via Wikimedia Commons

Oil spills are another kind of organic pollution. Oil spills can result from supertanker
accidents such as the Exxon Valdez in 1989, which spilled 10 million gallons of oil into
the rich ecosystem of offshore south Alaska and killed massive numbers of animals.
The largest marine oil spill was the Deepwater Horizon disaster, which began with a
natural gas explosion (see Figure 7.14.147.14.14 ) at an oil well 65 km offshore of
Louisiana and flowed for 3 months in 2010, releasing an estimated 200 million gallons
of oil. The worst oil spill ever occurred during the Persian Gulf war of 1991, when Iraq
deliberately dumped approximately 200 million gallons of oil in offshore Kuwait and set
more than 700 oil well fires that released enormous clouds of smoke and acid rain for
over nine months. During an oil spill on water, oil floats to the surface because it is less
dense than water, and the lightest hydrocarbons evaporate, decreasing the size of the
spill but polluting the air. Then, bacteria begin to decompose the remaining oil, in a
process that can take many years. After several months only about 15% of the original
volume may remain, but it is in thick asphalt lumps, a form that is particularly harmful
to birds, fish, and shellfish. Cleanup operations can include skimmer ships that vacuum
oil from the water surface (effective only for small spills), controlled burning (works only
in early stages before the light, ignitable part evaporates but also pollutes the
air), dispersants (detergents that break up oil to accelerate its decomposition, but some
dispersants may be toxic to the ecosystem), and bioremediation (adding
microorganisms that specialize in quickly decomposing oil, but this can disrupt the
natural ecosystem).

Figure 7.14.147.14.14 Deepwater Horizon Explosion. Boats fighting the fire from an
explosion at the Deepwater Horizon drilling rig in Gulf of Mexico offshore Louisiana on
April 20, 2010. Source: United States Coast Guard via Wikimedia Commons

Toxic chemicals involve many different kinds and sources, primarily from industry and
mining. General kinds of toxic chemicals include hazardous chemicals, which are a
wide variety of synthetic organic and inorganic chemicals such as acids, bases,
cyanide, and a class of compounds called persistent organic pollutants that
includes DDT (pesticide), dioxin (herbicide by-product), and PCBs (polychlorinated
biphenyls, which were used as a liquid insulator in electric transformers). Persistent
organic pollutants are long-lived in the environment, accumulate through the food chain
(bioaccumulation), and can be toxic. Another category of toxic chemicals
includes radioactive materials such as cesium, iodine, uranium, and radon gas, which
can result in long-term exposure to radioactivity if it gets into the body. A final group of
toxic chemicals is heavy metals such as lead, mercury, arsenic, cadmium, and
chromium, which can accumulate through the food chain. Heavy metals are commonly
produced by industry and at metallic ore mines. Arsenic and mercury are discussed in
more detail below. The US EPA regulates 83 contaminants in drinking water to ensure a
safe public water supply. Similarly, at the international level the World Health
Organization has drinking water standards for a variety of contaminants.

Arsenic (As) has been famous as an agent of death for many centuries. In large doses
arsenic causes cancer and can be fatal. Only recently have scientists recognized that
health problems can be caused by drinking small arsenic concentrations in water over a
long time. It attacks the central nervous system and can damage the respiratory system,
bladder, lungs, liver, and kidneys. It enters the water supply naturally from weathering of
As-rich minerals and from human activities such as coal burning and smelting of
metallic ores. The worst case of arsenic poisoning occurred in the densely populated
impoverished country of Bangladesh, which had experienced 100,000s of deaths from
diarrhea and cholera each year from drinking surface water contaminated with
pathogens due to improper sewage treatment. In the 1970s the United Nations provided
aid for millions of shallow water wells, which resulted in a dramatic drop in pathogenic
diseases. Unfortunately, many of the wells produced water naturally rich in arsenic.
Tragically, there are an estimated 77 million people (about half of the population) who
inadvertently may have been exposed to toxic levels of arsenic in Bangladesh as a
result. The World Health Organization has called it the largest mass poisoning of a
population in history.

Mercury (Hg) is used in a variety of electrical products, such as dry cell batteries,
fluorescent light bulbs, and switches, as well as in the manufacture of paint, paper, vinyl
chloride, and fungicides. In the methylmercury form (CH3Hg+) it is highly toxic; ≥ 1 ppb of
methylmercury represents water contaminated with mercury. Mercury concentrates in
the food chain, especially in fish, in a process caused biomagnification (see
Sidebar Biomagnification). It acts on the central nervous system and can cause loss of
sight, feeling, and hearing as well as nervousness, shakiness, and death. Like arsenic,
mercury enters the water supply naturally from weathering of Hg-rich minerals and from
human activities such as coal burning and metal processing. A famous mercury
poisoning case in Minamata, Japan involved methylmercury-rich industrial discharge
that caused high Hg levels in fish. People in the local fishing villages ate fish up to three
times per day for over 30 years, which resulted in over 2,000 deaths. During that time
the responsible company and national government did little to mitigate, help alleviate,
or even acknowledge the problem.

Biomagnification

Biomagnification represents the processes in an ecosystem that cause greater

concentrations of a chemical, such as methylmercury, in organisms higher up the food
chain. Mercury and methylmercury are present in only very small concentrations in
seawater; however, at the base of the food chain algae absorb methylmercury. Then,
small fish eat the algae, large fish and other organisms higher in the food chain eat the
small fish, and so on. Fish and other aquatic organisms absorb methylmercury rapidly
but eliminate it slowly from the body. Therefore, each step up the food chain increases
the concentration from the step below (see Figure 7.14.157.14.15). Largemouth bass
can concentrate methylmercury up to 10 million times over the water concentration and
fish-eating birds can concentrate it even higher. Other chemicals that exhibit
biomagnification are DDT, PCBs, and arsenic.

Figure 7.14.157.14.15 An illustrative example of

biomagnification of mercury from water through the food chain and into a bird's
egg. Source: U.S. Geological Survey

Other water pollutants include sediment and heat. Muddy water is bad for drinking but
even worse for underwater plants that need sunlight for photosynthesis. Much of the
sediment in water bodies is derived from the erosion of soil, so it also represents a loss
of agricultural productivity. Thermal pollution involves the release of heated waters from
power plants and industry to surface water, causing a drop in the dissolved O2 content,
which can stress fish.

Hard water contains abundant calcium and magnesium, which reduces its ability to
develop soapsuds and enhances scale (calcium and magnesium carbonate minerals)
formation on hot water equipment. Water softeners remove calcium and magnesium,
which allows the water to lather easily and resist scale formation. Hard water develops
naturally from the dissolution of calcium and magnesium carbonate minerals in soil; it
does not have negative health effects in people.

Groundwater pollution can occur from underground sources and all of the pollution
sources that contaminate surface waters. Common sources of groundwater pollution
are leaking underground storage tanks for fuel, septic tanks, agricultural activity, and
landfills. Common groundwater pollutants include nitrate, pesticides, volatile organic
compounds, and petroleum products. Polluted groundwater can be a more serious
problem than polluted surface water because the pollution in groundwater may go
undetected for a long time because usually it moves very slowly. As a result, the
pollution in groundwater may create a contaminant plume, a large body of flowing
polluted groundwater (see Figure 7.14.157.14.15), making cleanup very costly. By the
time groundwater contamination is detected, the entity responsible for the pollution
may be bankrupt or nonexistent. Another troublesome feature of groundwater pollution
is that small amounts of certain pollutants, e.g., petroleum products and organic
solvents, can contaminate large areas. In Denver, Colorado 80 liters of several organic
solvents contaminated 4.5 trillion liters of groundwater and produced a 5 km long
contaminant plume. Most groundwater contamination occurs in shallow, unconfined
aquifers located near the contamination source. Confined aquifers are less susceptible
to pollution from the surface because of protection by the confining layer. A major
threat to groundwater quality is from underground fuel storage tanks. Fuel tanks
commonly are stored underground at gas stations to reduce explosion hazards. Before
1988 in the U.S. these storage tanks could be made of metal, which can corrode, leak,
and quickly contaminate local groundwater. Now, leak detectors are required and the
metal storage tanks are supposed to be protected from corrosion or replaced with
fiberglass tanks. Currently there are around 600,000 underground fuel storage tanks in
the U.S. and over 30% still do not comply with EPA regulations regarding either release
prevention or leak detection.

Figure 7.14.167.14.16 Contaminant Plume in Groundwater. Mapping how a

contaminant plume will migrate once it reaches groundwater requires understanding of
the pollutant's chemical properties, local soil characteristics, and how permeable the
aquifer is. Source: United States Geological Survey

Sustainable Solutions to the Water Pollution Crisis?

Resolution of the global water pollution crisis described at the beginning of this section
requires multiple approaches to improve the quality of our fresh water and move
towards sustainability. The most deadly form of water pollution, pathogenic
microorganisms that cause waterborne diseases, kills almost 2 million people in
underdeveloped countries every year. The best strategy for addressing this problem is
proper sewage (wastewater) treatment. Untreated sewage is not only a major cause of
pathogenic diseases, but also a major source of other pollutants, including oxygen-
demanding waste, plant nutrients (N and P), and toxic heavy metals. Wastewater
treatment is done at a sewage treatment plant in urban areas and through a septic tank
system in rural areas.

The main purpose of a sewage treatment plant is to remove organic matter (oxygen-
demanding waste) and kill bacteria; special methods also can be used to remove plant
nutrients and other pollutants. The numerous processing steps at a conventional
sewage treatment plant (see Figure 7.14.177.14.17) include pretreatment (screening
and removal of sand and gravel), primary treatment (settling or floatation to remove
organic solids, fat, and grease), secondary treatment (aerobic bacterial decomposition
of organic solids), tertiary treatment (bacterial decomposition of nutrients and
filtration), disinfection (treatment with chlorine, ozone, ultraviolet light, or bleach), and
either discharge to surface waters (usually a local river) or reuse for some other
purpose, such as irrigation, habitat preservation, and artificial groundwater recharge.
The concentrated organic solid produced during primary and secondarytreatment is
called sludge, which is treated in a variety of ways including landfill disposal,
incineration, use as fertilizer, and anaerobic bacterial decomposition, which is done in
the absence of oxygen. Anaerobic decomposition of sludge produces methane gas,
which can be used as an energy source. To reduce water pollution problems, separate
sewer systems (where street runoff goes to rivers and only wastewater goes to a
wastewater treatment plant) are much better than combined sewer systems, which can
overflow and release untreated sewage into surface waters during heavy rain. Some
cities such as Chicago, Illinois have constructed large underground caverns and also
use abandoned rock quarries to hold storm sewer overflow. After the rain stops, the
stored water goes to the sewage treatment plant for processing.
 Figure 7.14.177.14.17 Steps at a Sewage Treatment Plant. The numerous processing
steps at a conventional sewage treatment plant include pretreatment (screening and
removal of sand and gravel), primary treatment (settling or floatation to remove organic
solids, fat, and grease), secondary treatment (aerobic bacterial decomposition of
organic solids), tertiary treatment (bacterial decomposition of nutrients and filtration),
disinfection (treatment with chlorine, ozone, ultraviolet light, or bleach), and either
discharge to surface waters (usually a local river) or reuse for some other purpose, such
as irrigation, habitat preservation, and artificial groundwater recharge. Source: Leonard
G.via Wikipedia

A septic tank system is an individual sewage treatment system for homes in rural and
even some urban settings. The basic components of a septic tank system (see
Figure 7.14.187.14.18) include a sewer line from the house, a septic tank (a large
container where sludge settles to the bottom and microorganisms decompose the
organic solids anaerobically), and the drain field (network of perforated pipes where the
clarified water seeps into the soil and is further purified by bacteria). Water pollution
problems occur if the septic tank malfunctions, which usually occurs when a system is
established in the wrong type of soil or maintained poorly.
 Figure 7.14.187.14.18 Sept
ic System. Septic tank system for sewage treatment. Source: United States Geological
Survey

For many developing countries, financial aid is necessary to build adequate sewage
treatment facilities; however, the World Health Organization estimates an estimated
cost savings of between $3 and $34 for every $1 invested in clean water delivery and
sanitation (Water for Life, 2005). The cost savings are from health care savings, gains in
work and school productivity, and deaths prevented. Simple and inexpensive
techniques for treating water at home include chlorination, filters, and solar
disinfection. Another alternative is to use constructed wetlands technology (marshes
built to treat contaminated water), which is simpler and cheaper than a conventional
sewage treatment plant.

Bottled water is not a sustainable solution to the water crisis, despite exponential
growth in popularity in the U.S. and the world. Bottled water is not necessarily any safer
than the U.S. public water supply, it costs on average about 700 times more than U.S.
tap water, and every year it uses approximately 200 billion plastic and glass bottles that
have a relatively low rate of recycling. Compared to tap water, it uses much more
energy, mainly in bottle manufacturing and long-distance transportation. If you don’t
like the taste of your tap water, then please use a water filter instead of bottled water!

Figure 7.14.197.14.19 Storm Drain. Curbside storm drain receiving urban

runoff. Source: By Robert Lawton via Wikimedia Commons

Additional sustainable solutions to the water pollution crisis include legislation to

eliminate or greatly reduce point sources of water pollution. In the U.S., the Clean Water
Act of 1972 and later amendments led to major improvements in water quality (see
Sidebar Clean Water Act). Nonpoint sources of water pollution, e.g., agricultural runoff
and urban runoff (see Figure 7.14.197.14.19), are much harder to regulate because of
their widespread, diffuse nature. There are many construction and agricultural practices
that reduce polluted runoff including no-till farming and sediment traps. Artificial
aeration or mechanical mixing can remediate lakes with oxygen depletion. Specific
things that we can do to reduce urban runoff include the following: keep soil, leaves,
and grass clippings off driveways, sidewalks, and streets; don't pour used motor oil,
antifreeze, paints, pesticides, or any household hazardous chemical down the storm
sewer or drain; recycle used motor oil; use hazardous waste disposal programs offered
by the community; compost your organic waste; don't use fertilizers and herbicides on
your lawn; and flush pet waste down the toilet.

Clean Water Act

During the early 1900s rapid industrialization in the U.S. resulted in widespread water
pollution due to free discharge of waste into surface waters. The Cuyahoga River in
northeast Ohio caught fire numerous times (see Figure 7.14.207.14.20), including a
famous fire in 1969 that caught the nation’s attention. In 1972 Congress passed one of
the most important environmental laws in U.S. history, the Federal Water Pollution
Control Act, which is more commonly called the Clean Water Act. The purpose of the
Clean Water Act and later amendments is to maintain and restore water quality, or in
simpler terms to make our water swimmable and fishable. It became illegal to dump
pollution into surface water unless there was formal permission and U.S. water quality
improved significantly as a result. More progress is needed because currently the EPA
considers over 40,000 U.S. water bodies as impaired, most commonly due to
pathogens, metals, plant nutrients, and oxygen depletion. Another concern is
protecting groundwater quality, which is not yet addressed sufficiently by federal law.

Figure 7.14.207
.14.20 Cuyahoga River on Fire. Source: National Oceanic and Atmospheric

Sometimes slow flow through a soil can naturally purify groundwater because some
pollutants, such as P, pesticides, and heavy metals, chemically bind with surfaces of
soil clays and iron oxides. Other pollutants are not retained by soil particles: These
include N, road salt, gasoline fuel, the herbicide atrazine, tetrachloroethylene (a
carcinogenic cleaning solvent used in dry cleaning), and vinyl chloride. In other cases,
slow groundwater flow can allow bacteria to decompose dead organic matter and
certain pesticides. There are many other ways to remediate polluted groundwater.
Sometimes the best solution is to stop the pollution source and allow natural cleanup.
Specific treatment methods depend on the geology, hydrology, and pollutant because
some light contaminants flow on top of groundwater, others dissolve and flow with
groundwater, and dense contaminants can sink below groundwater. A common cleanup
method called pump and treat involves pumping out the contaminated groundwater
and treating it by oxidation, filtration, or biological methods. Sometimes soil must be
excavated and sent to a landfill. In-situ treatment methods include adding chemicals to
immobilize heavy metals, creating a permeable reaction zone with metallic iron that
can destroy organic solvents, or using bioremediation by adding oxygen or nutrients to
stimulate growth of microorganisms.