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Glossary
Water Quality
Glossary
Action Level: The level of
lead or copper which, if exceeded, triggers treatment or other requirements that
a water system must follow.
Acute Health Effect: An immediate (i.e. within hours or days) effect that
may result from exposure to certain drinking water contaminants (e.g.,
pathogens).
Aquifer: A natural underground layer, often of sand or gravel, that
contains water.
Best Available Technology: The water treatment(s) that EPA certifies to
be the most effective for removing a contaminant.
Chronic Health Effect: The possible result of exposure over many years to
a drinking water contaminant at levels above its MCL.
Coliform: A group of related bacteria whose presence in drinking water
may indicate contamination by disease-causing microorganisms.
Community Water System: A water system which supplies drinking water to
25 or more of the same people year-round in their residences.
Compliance: The act of meeting all state and federal drinking water
regulations.
Contaminant: Anything found in water (including microorganisms, minerals,
chemicals, radionuclides, etc.) which may be harmful to human health.
Cryptosporidium: A microorganism commonly found in lakes and rivers which
is highly resistant to disinfection. Cryptosporidium has caused several large
outbreaks of gastrointestinal illness, with symptoms that include diarrhea,
nausea, and/or stomach cramps. People with severely weakened immune systems
(that is, severely immuno-compromised) are likely to have more severe and more
persistent symptoms than healthy individuals.
Disinfectant: A chemical (commonly chlorine, chloramine, or ozone) or
physical process (e.g., ultraviolet light) that kills microorganisms such as
bacteria, viruses, and protozoa.
Distribution System: A network of pipes leading from a treatment plant to
customers' plumbing systems.
Exemption: State or EPA permission for a water system not to meet a
certain drinking water standard. An exemption allows a system additional time to
obtain financial assistance or make improvements in order to come into
compliance with the standard. The system must prove that: (1) there are
compelling reasons (including economic factors) why it cannot meet a MCL or
Treatment Technique; (2) it was in operation on the effective date of the
requirement, and (3) the exemption will not create an unreasonable risk to
public health. The state must set a schedule under which the water system will
comply with the standard for which it received an exemption.
Exposure:
Contact between a person and a chemical.
Exposures are calculated as the amount of chemical available for absorption by a
person.
Finished Water: Water that
has been treated and is ready to be delivered to customers.
Giardia lamblia: A protozoan frequently
found in rivers and lakes, which can survive in water
for 1 to 3 months, associated with the disease giardiasis. Ingestion of this
protozoan in contaminated drinking water, exposure from person-to-person
contact, and other exposure routes may cause giardiasis. The symptoms of this
gastrointestinal disease may persist for weeks or months and include diarrhea,
fatigue, and cramps.
Ground Water: The water that systems pump and treat from aquifers
(natural reservoirs below the earth's surface).
Health Advisory: An EPA document that provides guidance and information
on contaminants that can affect human health and that may occur in drinking
water, but which EPA does not currently regulate in drinking water.
Inorganic Contaminants: Mineral-based compounds such as metals, nitrates,
and asbestos. These contaminants are naturally-occurring in some water, but can
also get into water through farming, chemical manufacturing, and other human
activities. EPA has set legal limits on 15 inorganic contaminants.
Maximum Contaminant Level (MCL): The highest level of a contaminant that
EPA allows in drinking water. MCLs ensure that drinking water does not pose
either a short-term or long-term health risk. EPA sets MCLs at levels that are
economically and technologically feasible. Some states set MCLs which are more
strict than EPA's.
Maximum Contaminant Level Goal (MCLG): The level of a contaminant at
which there would be no risk to human health. This goal is not always
economically or technologically feasible, and the goal is not legally
enforceable.
Microorganisms: Tiny living organisms that can be seen only with the aid
of a microscope. Some microorganisms can cause acute health problems when
consumed in drinking water. Also known as microbes.
Monitoring: Testing that water systems must perform to detect and measure
contaminants. A water system that does not follow EPA's monitoring methodology
or schedule is in violation, and may be subject to legal action.
Nitrates:
Inorganic compounds that can enter water
supplies from fertilizer runoff and sanitary wastewater discharges. Nitrates in
drinking water are associated with methemoglobinemia, or blue baby syndrome,
which results from interferences in the bloods ability to carry oxygen.
Non-Transient, Non-Community
Water System: A water system which supplies water to 25 or more of the same
people at least six months per year in places other than their residences. Some
examples are schools, factories, office buildings, and hospitals which have
their own water systems.
Organic Contaminants: Carbon-based chemicals, such as chlorohydrocarbons,
solvents and pesticides,
which can get into water through runoff from cropland or discharge from
factories. EPA has set legal limits on 56 organic contaminants.
Pathogen: A disease-causing organism.
Per capita:
Per person; generally used in expressions
of water use, gallons per capita per day (gpcd).
Point-of-Use Water Treatment:
Refers to devices used in the home or
office on a specific tap to provide additional drinking water treatment.
Point-of-Entry Water Treatment:
Refers to devices used in the home where
water pipes enter to provide additional treatment of drinking water used
throughout the home.
Primacy State: A State
that has the responsibility and authority to administer EPA's drinking water
regulations within its borders. The State must have rules at least as stringent
as EPA's.
Public Notification: An advisory that EPA requires a water system to
distribute to affected consumers when the system has violated MCLs or other
regulations. The notice advises consumers what precautions, if any, they should
take to protect their health.
Public Water System (PWS): Any water system which provides water to at
least 25 people for at least 60 days annually. There are more than 170,000 PWSs
providing water from wells, rivers and other sources to about 250 million
Americans. The others drink water from private wells. There are differing
standards for PWSs of different sizes and types.
Radionuclides: Elements that undergo a process of natural
decay. As radionuclides decay, they emit radiation in the form of alpha or beta
particles and gamma photons. Radiation can cause adverse health effects, such as
cancer, so limits are placed on radionuclide concentrations in drinking water.
Raw Water: Water in
its natural state, prior to any treatment for drinking.
Risk:
The potential for harm to people exposed
to chemicals. In order for there to be risk, there must be hazard and there must
be exposure.
Sample: The water that is
analyzed for the presence of EPA-regulated drinking water contaminants.
Depending on the regulation, EPA requires water systems and states to take
samples from source water, from water leaving the treatment facility, or from
the taps of selected consumers.
Sanitary Survey: An on-site review of the water sources, facilities,
equipment, operation, and maintenance of a public water systems for the purpose
of evaluating the adequacy of the facilities for producing and distributing safe
drinking water.
Secondary Drinking Water Standards: Non-enforceable federal guidelines
regarding cosmetic effects (such as tooth or skin discoloration) or aesthetic
effects (such as taste, odor, or color) of drinking water.
Sole Source Aquifer: An aquifer that supplies 50 percent or more of the
drinking water of an area.
Source Water: Water in its natural state, prior to any treatment for
drinking.
Surface Water: The water that systems pump and treat from sources open to
the atmosphere, such as rivers, lakes, and reservoirs.
Total Coliform:
Bacteria that are used as indicators of
fecal contaminants in drinking water.
Toxicity:
The property of a chemical to harm people
who come into contact with it.
Transient, Non-Community Water
System: A water system which provides water in a place such as a gas station
or campground where people do not remain for long periods of time. These systems
do not have to test or treat their water for contaminants which pose long-term
health risks because fewer than 25 people drink the water over a long period.
They still must test their water for microbes and several chemicals.
Treatment Technique: A specific treatment method required by
EPA to be used to control the level of a contaminant in drinking water. In
specific cases where EPA has determined it is not technically or economically
feasible to establish an MCL, EPA can instead specify a treatment technique.
Turbidity: The cloudy appearance of water caused by the presence of tiny
particles. High levels of turbidity may interfere with proper water treatment
and monitoring.
Variance: State or EPA permission not to meet a certain drinking water
standard. The water system must prove that: (1) it cannot meet a MCL, even while
using the best available treatment method, because of the characteristics of the
raw water, and (2) the variance will not create an unreasonable risk to public
health. The State or EPA must review, and allow public comment on, a variance
every three years. States can also grant variances to water systems that serve
small populations and which prove that they are unable to afford the required
treatment, an alternative water source, or otherwise comply with the standard.
Violation: A failure to meet any state or federal drinking water
regulation.
Volatile Organic Chemicals (V.O.C.'s):
Chemicals that, as liquid, evaporate into
the air.
Vulnerability Assessment:
An evaluation of drinking water source quality and its vulnerability to
contamination by pathogens and toxic chemicals.
Watershed: The land area from which water drains into a stream, river, or
reservoir.
Wellhead Protection Area: The area surrounding a drinking water well or
well field which is protected to prevent contamination of the well(s).
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