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INTRODUCTION
The quality of water is central to all of the roles that water
plays in our lives. From the beauty of natural waterways teeming with wildlife, to the vital livelihoods that clean rivers and
streams support, to the essential role that safe water plays in
drinking water and health – good water quality is fundamental
to the network of life and livelihood that water supports.
Water is the source of life on earth, and human civilizations
blossomed where there was reliable and clean freshwater.
Use of water by humans – for drinking, washing, and
recreation – requires water free from biological, chemical,
and physical sources of contamination. Plants, animals, and
the habitats that support biological diversity also need clean
water. Water of a certain quality is needed to grow food, to
power cities, and to run industries.
Water quality is as important as water quantity for satisfying
basic human and environmental needs, yet it has received
far less investment, scientific support, and public attention
in recent decades than water quantity, even though the two issues are closely linked. As part of the effort to improve
water quality, the United Nations Environment Programme
(UNEP) is supporting educational efforts around the world
to call attention to water quality challenges and solutions.
This summary assessment is part of those efforts and
synthesizes existing data from many public databases and
published reports.
Part 1 of the report provides an overview of current major
water quality contaminants and the human activities that
affect water quality. Part 2 details the impacts that poor
water quality has on the environment, human health, and
vulnerable communities, and quantifies the economic
costs of poor water quality. Part 3 of the report offers
insights into specific solutions available to address water
quality problems, and Part 4 explores the wide range of
mechanisms through which the solutions can be achieved.
Part 5 details key recommendations to improve and protect
water quality for the international community, national
governments, communities and households.
Contaminants in water
Both human activities and natural activities can change
the physical, chemical, and biological characteristics of
water, and will have specific ramifications for human and
ecosystem health. Water quality is affected by changes in
nutrients, sedimentation, temperature, pH, heavy metals,
non-metallic toxins, persistent organics and pesticides,
and biological factors, among many other factors (Carr and
Neary 2008). Following are brief discussions of these major
contaminants.
Many contaminants combine synergistically to cause worse,
or different, impacts than the cumulative effects of a single
pollutant. Continued inputs of contaminants will ultimately
exceed an ecosystem’s resilience, leading to dramatic,
non-linear changes that may be impossible to reverse (MA
2005a). For example, the extinction of all 24 species of fish
endemic to the Aral Sea resulted from dramatic increases
in salinity as inflows of freshwater dropped. While some still
hold out hope that it may be possible to restore Aral Sea
salinity to previous levels, there is no way to reverse the
extinction events that occurred. Another example of such
threshold-type changes is the creation of toxic algal blooms
(see Lake Atitlán case study, below), with direct and indirect
economic impacts on local populations.
Nutrients
Nutrient enrichment has become the planet’s most
widespread water quality problem (UN WWAP 2009).
Most often associated with nitrogen and phosphorus
from agricultural runoff, but also caused by human and
industrial waste, nutrient enrichment can increase rates of
primary productivity (the production of plant matter through
photosynthesis) to excessive levels, leading to overgrowth
of vascular plants (e.g. water hyacinth), algal blooms, and
the depletion of dissolved oxygen in the water column,
which can stress or kill aquatic organisms. Some algae
(cyanobacteria) can produce toxins that can affect humans,
livestock, and wildlife that ingest or are exposed to waters
with high levels of algal production. Nutrient enrichment can
also cause acidification of freshwater ecosystems, impacting
biodiversity (MA 2005b). Over the long term, nutrient
enrichment can deplete oxygen levels and eliminate species
with higher oxygen requirements, such as many species
of fish, affecting the structure and diversity of ecosystems
(Carpenter et al. 1998). Some lakes and ponds have
become so hypereutrophic (nutrient rich and oxygen poor)
due to nutrient inputs that all macro-organisms have been
eliminated.
Erosion and sedimentation
Erosion is a natural process that provides sediments
and organic matter to water systems. In many regions,
human activities have altered natural erosion rates and
greatly altered the volume, rate, and timing of sediment
entering streams and lakes, affecting physical and chemical
processes and species’ adaptations to pre-existing
sediment regimes. Increased sedimentation can decrease
primary productivity, decrease and impair spawning
habitat, and harm fish, plants, and benthic (bottomdwelling) invertebrates. Fine sediments can attract nutrients
such as phosphorus and toxic contaminants such as
pesticides, altering water chemistry (Carr and Neary 2008).
Dams and other infrastructure can dramatically degrade
a stream’s natural sediment transport function, starving
downstream reaches of needed nutrient and chemical
inputs. For example, the construction of major dams on the
Yangtze River has had a noticeable impact on sediment
load reaching the East China Sea according to Chinese
scientists. In recent years, sediment reaching Datong, near
the Yangtze’s delta, dropped to only 33 percent of the 1950-1986 levels (Xu et al. 2006). Among the consequences
of this drop in sediment are growing coastal erosion and a
change in the ecological characteristics and productivity of
the East China Sea (Xu et al. 2006).
Water temperature
Water temperature plays an important role in signaling
biological functions such as spawning and migration,
and in affecting metabolic rates in aquatic organisms.
Altering natural water temperature cycles can impair
reproductive success and growth patterns, leading to
long-term population declines in fisheries and other classes
of organisms. Warmer water holds less oxygen, impairing
metabolic function and reducing fitness. Such impacts can
be especially severe downstream of thermal or nuclear
power generation facilities or industrial activities, where the
return of water to the streams may be substantially warmer
than ecosystems are able to absorb (Carr and Neary 2008).
Acidification
The pH of different aquatic ecosystems determines the
health and biological characteristics of those systems. A
range of industrial activities, including especially mining and
power production from fossil fuels, can cause localized
acidification of freshwater systems. Acid rain, caused
predominantly by the interaction of emissions from fossilfuel combustion and atmospheric processes, can affect
large regions. Acidification disproportionately affects young
organisms, which tend to be less tolerant of low pH. Lower
pH can also mobilize metals from natural soils, such as
aluminum, leading to additional stresses or fatalities among
aquatic species. Acidification is widespread, especially
downwind of power plants emitting large quantities of
nitrogen and sulfur dioxides, or downstream of mines
releasing contaminated groundwater. According to the US
Environmental Protection Agency, for example, more than
90 percent of the streams in the Pine Barrens, a wetlands
region in the eastern United States, are acidic as a result of
upwind energy systems, particularly coal-fired power plants
(US EPA 2009a).
Salinity
Freshwater plant and animal species typically do not tolerate
high salinity. Various actions, often but not exclusively
anthropogenic, can cause salts to build up in the water.
These include agricultural drainage from high-salt soils,
groundwater discharge from oil and gas drilling or other
pumping operations, various industrial activities, and some
municipal water-treatment operations. Additionally, the
chemical nature of the salts introduced by human activities
may differ from those occurring naturally; for example, there
may be higher ratios of potassium than sodium salts. Rising
salinity can stress some freshwater organisms, affecting
metabolic function and oxygen saturation levels. Rising
salinity can also alter riparian and emergent vegetation,
affect the characteristics of natural wetlands and marshes,
decrease habitat for some aquatic species, and reduce
agricultural productivity and crop yields (Carr and Neary
2008).
Pathogenic organisms
One of the most widespread and serious classes of water
quality contaminants, especially in areas where access
to safe, clean water is limited, is pathogenic organisms:
bacteria, protozoa, and viruses. These organisms pose one
of the leading global human health hazards. The greatest
risk of microbial contamination comes from consuming
water contaminated with pathogens from human or animal
feces (Carr and Neary 2008). In addition to microorganisms
introduced into waters through human or animal fecal
contamination, a number of pathogenic microorganisms
are free-living in certain areas or are, once introduced,
capable of colonizing a new environment. These free-living
pathogens, like some Vibriobacterial species and a few
types of amoebas, can cause major health problems in
those exposed, including intestinal infections, amoebic
encephalitis, amoebic meningitis, and occasional death
(WHO 2008). Viruses and protozoa also pose human health
risks, including Cryptosporidiumand Giardia, Guinea worm,
and others.
Trace metals
Trace metals, such as arsenic, zinc, copper, and selenium,
are naturally found in many different waters. Some human
activities like mining, industry, and agriculture can lead to
an increase in the mobilization of these trace metals out of soils or waste products into fresh waters. Even at extremely
low concentrations, such additional materials can be
toxic to aquatic organisms or can impair reproductive and
other functions. In the early 1980s, high concentrations of
selenium in agriculture drainage water discharged to the
Kesterson National Wildlife Refuge in California extirpated all
but one species of fish and caused widespread bird dieoffs, as well as severe deformities in several bird species
(Ohlendorf 1989).
Human-produced chemicals and
other toxins
Diverse human-produced organic chemicals can enter
surface and groundwater through human activities, including
pesticide use and industrial processes, and as breakdown
products of other chemicals (Carr and Neary 2008). Many of
these pollutants, including pesticides and other non-metallic
toxins, are used globally, persist in the environment, and
can be transported long ranges to regions where they have
never been produced (UNEP 2009).
Organic contaminants (sometimes called “persistent
organic pollutants”, or POPS), such as certain pesticides,
are commonly found to be contaminating groundwater by
leaching through the soil and surface waters through runoff
from agricultural and urban landscapes. DDT, a pesticide
that has been banned in many countries but is still used
for malaria control in countries throughout Africa, Asia, and
Latin America (Jaga and Dharmani 2003), remains persistent
in the environment and is resistant to complete degradation
by microorganisms (WHO 2004a). Even in countries where
DDT has been banned for decades, it is still consistently
found in sediments, waterways, and groundwater. For
some of these materials, non-lethal doses may be ingested
by invertebrates and stored in their tissues, but as larger
organisms consume these prey species, the amounts of
pesticides and other materials bioaccumulate, eventually to
toxic levels. Some pesticides break down in the environment
over time, but breakdown products may also be toxic
and can concentrate in sediments, to be released in large
volumes during scouring events or other disturbances.
Other organic pollutants, such as dioxins, furans, and
polychlorinated biphenyls (PCBs) are the byproduct of
industrial processes and enter the environment both through
their use and disposal (UNEP 1998). Such materials have
become an emerging threat, with possible long-term
degradation of freshwater and other ecosystems. PCB
contamination has been widespread around the world. In
New York, for instance, over a million pounds (over 550
metric tonnes) of PCBs were dumped into the Hudson River
in the mid-20th century. High PCB levels found in Hudson
River fish led to bans on fishing, and decades of remediation
efforts that continue to this day (US EPA 2009b).
Other emerging contaminants (addressed in more detail
below) include endocrine disruptors, pharmaceuticals, and
personal care products that may not be removed by existing
wastewater treatment operations and end up entering freshwater systems. These contaminants can impair reproductive
success in birds and fish and feminize male offspring, and
they may have other impacts yet to be detected.
Introduced species and other biological
disruptions
The rising incidence of invasive species displacing endemics
and altering water chemistry and local foodwebs increasingly
affects freshwater systems and should be considered
a water quality problem (Carr and Neary 2008). Aquatic
species have in many cases been introduced deliberately
into distant ecosystems for recreational, economic, or other
purposes. In many instances, these introductions have
decimated endemic fish and other aquatic organisms, and
they can also degrade local watersheds. Other species have
invaded inadvertently, transported on the hulls of recreational
watercraft or in the bilgewater of commercial boat traffic.
For example, invasive species such as zebra (Dreissena
polymorpha) and quagga (D. bugensis) mussels have
devastated local ecosystems, altering nutrient cycles and
pushing endemic species to the brink of extinction. Mussels
in particular also pose grave threats to human infrastructure,
clogging pumps and intakes and choking canals, leading to
costly and continual maintenance challenges.
In South Africa, invasive plant species have altered local
water quality and reduced water quantity as well by increasing evapotranspiration rates in watersheds. According to
the South African Department of Water Affairs and Forestry,
invasive alien species are causing billions of rands of damage to the country’s economy every year, and are the single
biggest threat to the country’s biodiversity. Since its inception in 1995, the Working for Water Programme has cleared
more than one million hectares of invasive alien plants while
also providing jobs and training to approximately 20,000
people from among the most marginalized sectors of society
per annum (SA DWAF 2009). In the United States, the invasion of some species of mussels has led to additional costs
exceeding a billion dollars annually to the water power industry and in impacts on local ecosystems (De Leon 2008).
Emerging contaminants
A growing number of contaminants are being detected in
water for two reasons: new chemicals are being introduced
for agricultural, industrial, and household use and can enter
and persist in the environment, and new testing techniques
allow contaminants to be detected at lower and lower levels.
Substances can enter the environment through intentional,
measured releases (pesticide applications); as regulated or unregulated industrial and agricultural by-products; through
accidental spills or leaks during the manufacturing and
storage of these chemicals; or as household waste (Carr and
Neary 2008). In agricultural settings, over-spraying and longrange transport can cause these substances to be found
long distances from the initial point of application.
About 700 new chemicals are introduced into commerce
each year in the United States alone (Stephenson 2009),
and worldwide, pesticide application is estimated to be
approximately 5 billion pounds (over 2 million metric tonnes)
(PAN 2009). Despite their widespread use, the prevalence,
transport, and fate of many of these new chemicals
remain largely unknown because until recently, testing
techniques were unable to detect contaminants at the low
concentrations at which they are present in the environment
(Carr and Neary 2008).
Synthetic chemicals known as endocrine disruptors are
an excellent example of emerging contaminants where the
threats and consequences for water quality, human health,
and the environment are still not fully understood. Endocrine
disruptors – chemicals that can interfere with hormone
action – have been identified among chemicals used in
agriculture, industry, and households, and for personal
care, including pesticides, disinfectants, plastic additives,
and pharmaceuticals like birth control pills. Many of these
endocrine-disruptors mimic or block other hormones in
the body, disrupting the development of the endocrine
system and the organs that respond to endocrine signals
in organisms indirectly exposed during early developmental
stages; these developmental effects are permanent and
irreversible (Colborn 1993). The effects of endocrine
disruptors on wildlife include the thinning of eggshells in
birds, inadequate parental behavior, cancerous growths,
and other effects (Carr and Neary 2008). For example, the
feminization of fish living downstream from wastewater
treatment plants has long been linked to estrogenic
pharmaceuticals (Sumpter 1995) and new studies have also
linked feminization of amphibians to endocrine disrupting
pesticides such as atrazine (Hayes et al. 2006).
The effects of these chemicals on humans and human
development are less well known; however, animal studies
suggest there is cause for concern, even at low doses. In
addition, research shows the effects may extend beyond the
exposed individual, particularly affecting fetuses of exposed
pregnant women and breastfed children. Recent reports also
show multi-generation effects of some endocrine disruptors,
through modification of genetic materials and other heritable
mechanisms (ES 2009).
Pharmaceuticals and personal care products are also
of increasing concern. These chemicals originate from
products like cosmetics, toiletries, and detergents, as
well as from pharmaceuticals ranging from painkillers
and antidepressants to hormone-replacement therapies
and chemotherapy agents (Carr and Neary 2008). These
chemicals enter the environment and waterways as
wastewater facilities are not equipped to remove them (Carr
and Neary 2008). While the low concentrations currently
present in waterways do not present any observable
acute health effects, they may present subtle behavioral
and reproductive problems for humans and wildlife (Carr
and Neary 2008), and there are likely synergistic impacts
when combined with other endocrine disruptors. As an
example, at concentrations of micrograms/L of the antibiotic
tetracycline one study found measurable negative impacts
on aquatic bacteria (Verma et al. 2007). New research is
needed to address these uncertainties.
In addition to emerging chemical contaminants, there is also
the threat of emerging pathogens – those that are appearing
in human populations for the first time, or have occurred
before but are increasing in incidence or are expanding into
areas where they have not been reported (WHO 2003a).
Not only do water-related diseases remain a leading cause
of global morbidity and mortality, but several studies have
confirmed that the variety of disease is expanding and
the incidence of many water-related microbial diseases is
increasing (WHO 2003a).
Pathogens can emerge as a result of new environments
or changes in environmental conditions, like dams and
irrigation projects; from the use of new technologies; and
from scientific advancements, such as the inappropriate
use of antibiotics, insecticides, and pesticides creating
resistant pathogen strains (WHO 2003a). In recent years,
175 species of infectious agents from 96 different genera
have been classified as emerging pathogens (WHO 2003a).
The emergence of new pathogens or the increase in their
incidence also threatens water quality.
Human activities that affect water quality
A wide range of human activities affect water quality.
Below, four major categories are discussed – agricultural
production, industrial and mining activities, water
infrastructure, and the direct disposal of untreated or partly
treated human wastes into water systems – along with the
impacts these activities have on water quality. There are
also key processes that have and will continue to impact
water quality: these are population growth, urbanization, and
climate change. These are described below.
Agriculture
The vast extent of agricultural activities around the world
contributes significantly to both economic productivity and water-pollutant loads. Since the 1970s, there has been
growing concern over the increases in nitrogen, phosphorus,
and pesticide runoff into surface and groundwater. Intensive
cultivation and growing concentrations of “factory” livestock
or aquaculture operations have also long been known to
produce large non-point source contributions of pollutants to
surface and groundwater pollution (Ignazi 1993). A comparison of domestic, industrial, and agricultural sources of pollution from the coastal zone of Mediterranean countries found
that agriculture was the leading source of phosphorus compounds and sediment (UNEP 1996a). Furthermore, nitrate
is the most common chemical contaminant in the world’s
groundwater and aquifers (Spalding and Exner 1993). According to various surveys in India and Africa, 20-50 percent
of wells contain nitrate levels greater than 50 milligrams per
liter, and in some cases as high as several hundred milligrams per liter (cited in FAO 1996). Recent data from UNEP
GEMS/Water shows that mean nitrate concentrations have
increased in the last decade in watersheds in the Americas,
Europe, Australasia, and most significantly, in Africa and the
eastern Mediterranean (Figure 1).
Beyond nitrate contamination, agricultural activities are also
linked to the salinization of surface water, eutrophication
(excess nutrients), pesticides in runoff, and altered erosion
and sedimentation patterns. The Food and Agriculture
Organization (FAO 1996) has compiled a summary of
common agricultural impacts on surface water and
groundwater resources (Table 1).
Industry and energy production
Industrial activities are a significant and growing cause
of poor water quality. Industry and energy production
use accounts for nearly 20 percent of total global water
withdrawals (UN WWAP 2009), and this water is typically
returned to its source in a degraded condition. Wastewater
from industrial facilities such as power plants, paper mills,
pharmaceutical manufacturers, semiconductor fabrication
plants, chemical plants, petroleum refineries, and bottling
facilities, and processes such as mining and drilling, all
contribute to poor water quality around the world. Industrial
wastewater can contain a number of different pollutants,
including:
• Microbiological contaminants like bacteria, viruses, and
protozoa;
• Chemicals from industrial activities like solvents and
organic and inorganic pesticides, polychlorinated
biphenyls (PCBs), asbestos, and many more;
• Metals such as lead, mercury, zinc, copper, and many
others;
