Health Effects of Drinking Water Contaminants
Sandra A. Zaslow and Glenda M. Herman
Extension Housing Specialists
Published by: North Carolina Cooperative Extension
Publication Number: HE-393
Last Electronic Revision: March 1996 (JWM)
People are increasingly concerned about the
safety of their drinking water. As improvements
in analytical methods allow us to detect impurities at very low concentrations in water, water
supplies once considered pure are found to have
contaminants. We cannot expect pure water, but
we want safe water.
The health effects of some contaminants in
drinking water are not well understood, but the
presence of contaminants does not mean that
your health will be harmed. In North Carolina,
drinking water is generally of high quality and
free from significant contamination. Public water
supplies are tested, and regulated to ensure that
our water remains free from unsafe levels of
contamination. Small private water supplies,
including wells, are not regulated by drinking
water standards, and the owner must take steps
to test and treat the water as needed to avoid
possible health risks.
What is in your drinking water? The only
way to know is to have it tested.
Drinking water can become contaminated at
the original water source, during treatment, or
during distribution to the home.
- If your water comes from surface water
(river or lake), it can be exposed to acid rain,
storm water runoff, pesticide runoff, and industrial waste. This water is cleansed somewhat by exposure to sunlight, aeration, and
micro-organisms in the water.
- If your water comes from groundwater (private wells and some public water supplies),
it generally takes longer to become contaminated but the natural cleansing process also
may take much longer. Groundwater moves
slowly and is not exposed to sunlight,
aeration, or aerobic (requiring oxygen)
micro-organisms. Groundwater can be
contaminated by disease-producing pathogens, leachate from landfills and septic
systems, careless disposal of hazardous
household products, agricultural chemicals,
and leaking underground storage tanks.
Possible Health Effects
The levels of contaminants in drinking water
are seldom high enough to cause acute (immediate) health effects. Examples of acute health
effects are nausea, lung irritation, skin rash,
vomiting, dizziness, and even death.
Contaminants are more likely to cause
chronic health effects - effects that occur long
after repeated exposure to small amounts of a
chemical. Examples of chronic health effects
include cancer, liver and kidney damage, disorders of the nervous system, damage to the
immune system, and birth defects.
Evidence relating chronic health effects to
specific drinking water contaminants is limited.
In the absence of exact scientific information, scientists predict the likely adverse effects of
chemicals in drinking water using human data
from clinical reports and epidemiological studies, and laboratory animal studies.
Drinking Water Standards
The Safe Water Drinking Act of 1974 directed
the U.S. Environmental Protection Agency (EPA)
to ensure that public water systems (systems
serving more than 25 people) and noncommunity water systems (hotels, campsites, restau-
rants, migrant workers' encampments, and
work sites) meet minimum standards for protecting public health. Its main provisions
directed the EPA to establish minimum drinking
water standards to limit the amounts of various
contaminants found in drinking water. Because
of growing concerns about the safety of the
water supply, amendments were made to
strengthen this law in 1986. These amendments
required the EPA to do the following:
- Develop a maximum contaminant level goal
(MCLG) and a maximum contarninant level
(MCL) for all regulated contaminants.
MCLGs are nonenforceable health-based
goals and represent the maximum level of a
contaminant that is expected not to cause
any adverse health effects over a lifetime.
MCLs are enforceable contaminant levels.
They are set as close to the MCLG as possible and are based on protecting public
health within economical and technical
- Increase the number of regulated contaminants to a total of 83 by June, 1989. MCLs
must be set for an additional 25 contaminants every 3 years thereafter.
- Set required schedules for water systems to
monitor for contaminants in drinking water.
- Identify best available technologies (BATS)
for removing excess contaminants from
water, based on efficiency, availability, and
- Issue variances and exceptions to systems
that cannot comply with MCLs despite the
application of BATS, unless an "unreasonable risk" to health exists. "Unreasonable
risk" has not yet been defined.
- Provide for public notification when drinking water standards are violated.
- Ban the use of lead pipes, solder, fittings,
and flux in public water systems.
- Bolster enforcement of penalties for violators
of drinking water standards at the state and
- Provide for protection of groundwater
Contaminants are regulated when they occur
in drinking water supplies and are expected to
threaten public health. Most levels established
by the EPA allow a sufficient margin of safety,
but acceptable contaminant levels vary widely
among individuals and population groups. For
example, high sodium levels, harmless for most
people, can be dangerous for the elderly, people
with high blood pressure, pregnant women, and
people having difficulty in excreting sodium.
North Carolina has adopted EPA standards
and the state has responsibility for enforcing
drinking water standards.
Every day, you can be exposed to combinations
of many toxic substances and these substances may interact.
What is in water may represent only a small
part of your overall exposure to a specific contaminant.
Scientists who investigate how contaminants affect human health get information
in several ways. They may study how a toxic
substance has affected people in a community
over time. In some cases, this can show relationship between exposure to a contaminant and
a health effect They may also use animal studies
to collect information on the acute and chronic
Research helps scientists determine toxic
doses and levels below which toxic effects are
not observed. For noncancer-causing toxic substances, scientists use "acceptable daily intake"
to estimate risk. The acceptable daily intake is
the amount of a contaminant or toxic substance
that humans can consume daily for a lifetime
without any known ill effects. It includes a
margin of safety. For a cancer-causing substance,
no safe level has been set. Toxicity is estimated
by calculating a risk estimate, or the concentration of a substance that presents the least
acceptable risk. In the case of cancer-causing toxins,
regulations are based on a level of risk that is
acceptable, not a safe amount or concentration of
Four Groups of Contaminants
Microbial Pathogens. Pathogens in drinking
water are serious health risks. Pathogens are
disease-producing micro-organisms, which include bacteria (such as giardia lamblia), viruses,
and parasites. They get into drinking water
when the water source is contaminated by
sewage and animal waste, or when wells are
improperly sealed and constructed. They can
cause gastroenteritis, salmonella infection,
dysentery, shigellosis, hepatitis, and giardiasis
(a gastrointestinal infection causing diarrhea,
abdominal cramps, and gas). The presence of
coliform bacteria, which is generally a harmless
bacteria, may indicate other contamination to the
drinking water system.
Organics. People worry the most about
potentially toxic chemicals and metals in water.
Only a few of the toxic organic chemicals that
occur drinking water are regulated by drinking
water standards. This group of contaminants
- Trihalomthanes (THMs), which are formed
when chlorine in treated drinking water
combines with naturally occurring organic
- Pesticides, including herbicides, insecticides,
- Volatile organic chemicals (VOCs), which
include solvents, degreasers, adhesives,
gasoline additives, and fuels additives. Some
of the common VOCs are: benzene, trichloroethylene (TCE), styrene, toluene, and vinyl
chloride. Possible chronic health effects
include cancer, central nervous system
disorders, liver and kidney damage, reproductive disorders, and birth defects.
Inorganics. These contaminants include toxic
metals like arsenic, barium, chromium, lead,
mercury, and silver. These metals can get into
your drinking water from natural sources,
industrial processes, and the materials used in
your plumbing system. Toxic metals are regulated in public water supplies because they can
cause acute poisoning, cancer, and other health
Nitrate is another inorganic contaminant.
The nitrate in mineral deposits, fertilizers,
sewage, and animal wastes can contaminate
water. Nitrate has been associated with "blue
baby syndrome" in infants.
Radioactive Elements. Radon is a radioactive contaminant that results from the decay of
uranium in soils and rocks. It is usually more of
a health concern when it enters a home as a soil
gas than when it occurs in water supplies.
Radon in air is associated with lung cancer.
As people hear about the possibility of
contaminants in their drinking water, they
worry about potential health effects.
Water supplies once considered to be pure may
have various contaminants, often from natural
sources. These are usually at levels below those
considered to be harmful.
If you are concerned, test your water. For
more information on water quality, testing, and
treatment, contact the Extension Center or health
department in your county or your physician.
Home Water Quality and Safety. Haman, Dorata Z.
and Boucher, Del B. Florida Cooperative Ex
tension Service. University of Florida. Pub.
Health Effects of Drinking Water Contaminants.
Stewart, Judith C., Lemley, Ann T., Hogan,
Sharon I. and Weismiller, Richard A. Cornell
University and the University of Maryland.
Fact Sheet 2.1989.
Drinking Water: Present Problems, Future Directions
. Nutrition Clinics. Woodruff, Sandra L.
Vol. 5, No. 2,1990: 1-21.
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