drinking water quality
RETURN TO HOME PAGE
The Importance of Our Drinking Water
Water is the most important element on which all life depends. The average adult body is approximately 55 to 60 percent water. As our population grows, the amount of water used for industry, farming and recreation also grows. Water is our most precious and indispensable resource. The scarcity of water and also its quality are becoming issues. Various chemicals have contaminated both surface and underground waters. Sewage, factory waste and toxins pollute our rivers and lakes and threaten our most important resource.
Collecting Data on Drinking
This website gives data and information on contaminants found in our
water systems. The data used comes from state drinking water programs that
collect it from the water suppliers. The data are routinely collected as part
of the monitoring requirements set out by the Environmental Protection Agency (EPA)
as well as other state agencies. Community water suppliers are required by law
to conduct regular water quality monitoring for impurities and report
the results to the state regulatory agency. The data are not collected
specifically to measure the level of exposure or to track changes in quality
over time. However, these data are the only set of data on drinking water
quality that are currently available for scientific research.
COMMUNITY WATER SYSTEMS
EPA sets rules for treating and checking on drinking water delivered by community water systems.
There are quality standards and monitoring requirements for over 90 substances. Treatment and
monitoring rules for these systems will vary from state to state. Programs at both the state and national
levels play an important role in ensuring high quality drinking water. By having quality standards and
monitoring requirements we protect the public's health.
Drinking water can be polluted by natural sources like bedrock, or
from man-made sources like chemicals or farming run-off. Pollution can happen
if there are new sources of contamination of the natural water sources that the
system uses. Also there are sometimes problems with the water treatment system
itself. The risk of developing a specific disease depends on many factors:
the specific contaminating substance; the level and potency of that substance;
the way that it enters the body, for example, drinking or showering; and the
person’s individual susceptibility. Elderly people, children and pregnant women
are more likely to suffer ill effects than the rest of the population.
Since pollution in a single system can expose so many people at
once, drinking water quality is an important public health issue. People can be
exposed to contaminants not only by drinking the water but also by eating foods
prepared with the water, breathing water droplets or chemicals released from
the water while showering or by absorbing chemicals through their skin while
DRINKING WATER MONITORING IN THE UNITED STATES
Community water systems are required to provide drinking water
that meets standards established under the Safe Drinking Water Act. EPA
establishes drinking water standards for individual substances and groups of substances.
Typically, EPA establishes Maximum Contaminant Levels (MCLs) and associated
compliance monitoring requirements. When it is not feasible to measure a
contaminant in drinking water, EPA establishes drinking water Treatment
Technique Requirements (TTR). These are requirements about the type of
treatment required and measures of how well these processes are working.
Compliance with MCLs and TTRs is the basis of determining whether the drinking
water meets public health standards.
MCLs and TTRs apply to all community water systems; however, the
associated monitoring requirements vary. Monitoring requirements are
contaminant-specific. Regulations and state drinking water agencies specify
sample location and acceptable analytical methods. The frequency of monitoring
for a substance may vary based on the type of source water and on the results
of previous samples. Monitoring may vary based on service population size and
water treatment used.
Drinking water standards and monitoring requirements are not fixed
or unchanging. New rules are developed for previously unregulated substances.
Also, EPA must periodically review and, if necessary, revise existing
regulations based on new information.
Arsenic is a toxic chemical element that is naturally found in the
Earth’s crust. There is a wide variation in the levels of arsenic found in
drinking water systems and private water supplies across the country. Arsenic can also be a byproduct of some farming and industrial
activities. It can enter drinking water through the ground or as run-off into
surface water sources.
MONITORING REQUIREMENTS FOR ARSENIC
All community water systems are required to monitor for arsenic at
the entry point to the distribution system; however, the frequency of
monitoring varies based on source water type and the level of arsenic observed
in past samples. Routine-required monitoring is annual for surface water and
once every three years for ground water, with quarterly monitoring once a
sample exceeds 10 parts per billion. With a state-granted monitoring
waiver, the sampling frequency can be reduced to once every nine years.
ARSENIC EXPOSURE AND RISK
Some people who drink water containing arsenic over many years
could experience skin damage or problems with their circulatory system, and may
have an increased risk of getting cancer. Health effects might include:
- Thickening and discoloration of the
skin, stomach pain, nausea, vomiting, diarrhea and liver
- Cardiovascular, pulmonary, immunological,
neurological, reproductive and endocrine effects
- Cancer of the bladder, lungs, skin, kidney, nasal passages, liver and prostate
ARSENIC EXPOSURE PREVENTION
If your water comes from a municipal or privately-owned water
company that meets the definition of a community water system, they are already
testing your water for arsenic. If you have your own household water supply,
you are responsible for testing it. Contact your local health department to
find out whether arsenic is a concern in your area. Your state’s drinking water
agency can give you names of laboratories that are certified to test drinking
DISINFECTION BYPRODUCTS (DBPs) AND YOUR HEALTH
Public water may contain
viruses and bacteria that can cause illness, such as gastrointestinal disorders
or diarrhea. Public water suppliers disinfect their water to kill these.
Chlorine is the most commonly used disinfectant, sometimes used in combination
with other disinfectants such as ozone, chloramine, chlorine dioxide and
The risk of illness from disinfectants
is much lower than the risk of illness from drinking most surface water or
ground water that has not been disinfected. The major health risks from DBPs
result from long-term exposures. EPA requires that water systems use treatment
methods to reduce disinfection byproducts and protect people from waterborne
disease and the harmful effects of disinfection byproducts.
DISINFECTION BYPRODUCT EXPOSURE AND RISK
When people consume
disinfection byproducts at high levels over many years, they increase their
risk of developing bladder cancer. Other health effects include rectal and
colon cancer. Adverse developmental and reproductive effects associated with
exposure to disinfection byproducts during pregnancy are also a concern.
There are two primary ways
that disinfection byproducts can get into your body:
Ingestion through your mouth: drinking water with DPBs
- Inhalation through your nose: some DBPs can be released into the air when you use your tap
water. This can happen when you are taking a shower or washing dishes. And the hotter the
water is, the more likely it is that DBPs will be released into the air. DBPs can also get into the
air when you boil your
tap water, such as when you make tea or soup.
DISINFECTION BYPRODUCTS PREVENTION
If your public water system
has notified you of a disinfection byproduct violation, it does not mean that
the people who consume the system's water will become sick or that your
exposure to DBPs has increased. EPA requires that water systems use treatment
methods to reduce the formation of disinfection byproducts and protect people
from disease and the harmful effects of disinfection byproducts.
NITRATES AND YOUR HEALTH
Nitrates and nitrites are
nitrogen-oxygen molecules which can combine with various compounds. Nitrates are
the form commonly found in water, often in areas where nitrogen-based fertilizers
are used. Vegetables and meat are the major sources of nitrate exposure. Nitrates and nitrites
originate in drinking water from nitrate-containing fertilizers, sewage and
septic tanks and decaying natural material such as animal waste. Nitrates are
very soluble in water, can easily migrate and do not bind to soils.
Nitrates/nitrites are likely to remain in water until consumed by plants or
The short-term risks of high
levels of nitrates include the potential for serious illness and sometimes
death. The serious illness in infants is due to the conversion of
nitrate to nitrite by the body, which can interfere with the oxygen-carrying
capacity of the child’s blood. This can be an acute condition in which health
deteriorates rapidly over a period of days. Symptoms include shortness of
breath and blueness of the skin. The
long-term risks are being investigated with possible
effects including adverse reproductive effects and some forms of cancer.
Tracking Drinking Water Quality
THE PURPOSE OF THESE INDICATORS IS TO PROVIDE INFORMATION ABOUT DRINKING
WATER QUALITY FROM A PUBLIC HEALTH PERSPECTIVE. THREE TYPES OF INDICATORS ARE USED:
1. Contextual Measures - The contextual measures show how many people drink water covered
under the Safe Drinking Water Act, which regulates contaminant levels in water. The
proportion of a state’s population served by community water supplies is estimated between
44 and 95
percent. This proportion provides a measure of the estimated proportion of people
in the state that are served by water that is being monitored for public health protection. This
also gives context to how much of the total population is represented by the
community water supplies included in the level of contaminant and potential population
2. Level of Contaminants in Drinking Water - These measures give the level of the
contaminant in the water served by community water systems showing the extent of
contamination across water systems. The level of the contaminants is measured in two ways:
in comparison to a benchmark level, such as the maximum contaminant level (MCL), and in
terms of average or
maximum contaminant concentrations.
3. Potential Population Exposure to Contaminants in Drinking Water - These measures
portray the potential public exposure to the four contaminants based on the observed levels of
the contaminants. This potential for exposure is measured in two ways: by the amount and
proportion of population that is provided water which meets a benchmark, usually the MCL,
and in terms of average or maximum contaminant concentration.