| Action level |
A specified
concentration of a contaminant in water. If this concentration is
reached or exceeded, certain actions (e.g., further treatment and
monitoring) must be taken to comply with a drinking water regulation.
|
| Back-siphonage |
A reversal of
the normal flow of water or other liquid caused by a negative-pressure
gradient (e.g., within a water system).
|
| Boil-water advisory |
A statement to the public advising that tap water must be boiled
before drinking it.
|
| Cercarial dermatitis |
Dermatitis caused by contact with the
cercariae (larval stage) of certain species of schistosomes whose
normal hosts are birds and nonhuman mammals. |
| Class |
Waterborne-disease outbreaks are classified according to the strength
of the epidemiologic and water-quality data implicating water as the
source of the outbreak (see Table 1). |
| Coagulation |
The process of adding chemicals to water to destabilize charges on
naturally occurring particles to facilitate their subsequent
aggregation and removal by flocculation or filtration. |
| Coliforms |
All aerobic and facultative anaerobic, gram-negative, nonspore-forming,
rod-shaped bacteria that ferment lactose with gas formation within 48
hours at 95° F (35°C).
|
| Community water system |
A public water system that serves year-round residents of a community,
subdivision, or mobile home park that has >15 service connections or
an average of >25 residents for >60 days/year.
|
| Contact time |
The length of time water is exposed to a disinfectant (e.g., chlorine
contact time).
|
| Cross-connection |
Any actual or potential connection between a drinking water supply and
a possible source of contamination or pollution (e.g., a wastewater
line).
|
| Cyst |
The infectious stage of Giardia intestinalis and certain other
protozoan parasites that have protective walls that facilitate their
survival in water and other environments.
|
| Disinfection by-products |
Chemicals formed in water through reactions between organic matter and
disinfectants.
|
| Distribution system |
Water pipes, storage reservoirs, tanks, and other means used to
deliver drinking water to consumers or store it before delivery.
|
| Excystation |
The release of the internal (i.e., encysted) contents (e.g.,
trophozoites or sporozoites) from cysts or oocysts.
|
| Fecal coliforms |
Coliforms that grow and produce gas at 112.1 º F
(44.5 º C) within 24 hours.
|
| Filter backwash |
Water containing the material obtained by reversing the flow of water
through a filter to dislodge the particles that have been retained on
it.
|
| Filtration |
The process of removing suspended particles from water by passing it
through one or more permeable membranes or media of limited diameter
(e.g., sand, anthracite, or diatomaceous earth). |
| Finished water |
The water (e.g., drinking water) delivered to the distribution system
after treatment, if any.
|
| Flocculation |
The water-treatment process after coagulation that uses gentle
stirring to cause suspended particles to form larger, aggregated
masses (floc). The aggregates are removed from the water by a
separation process (e.g., sedimentation, flotation, or filtration). |
| Free, residual chlorine level |
The concentration of chlorine in water that is not combined with other
constituents, thus serving as an effective disinfectant.
|
| Groundwater system |
A system that uses water extracted from the ground (i.e., a well or
spring).
|
| Groundwater under the direct
influence of surface water |
Any water beneath the surface of the ground with substantial
occurrence of insects or other macrooganisms, algae, or large-diameter
pathogens (e.g., Giardia intestinalis or — for subpart H
systems serving >10,0000 persons only — Cryptosporidium parvum,
or substantial and relatively rapid shifts in water characteristics
(e.g., turbidity, temperature, conductivity, or pH that closely
correlate to climatological or surface water conditions. Direct
influence must be determined for individual sources in accordance with
criteria established by the state. The state determination of direct
influence might be based on site-specific measurements of water
quality or documentation of well construction characteristics and
geology with field evaluation. |
| Heterotrophic microflora |
Microorganisms that use organic material for energy and growth.
|
| Infant water |
Bottled waters that are marketed for direct consumption by infants or
use in mixing with infant formula.
|
| Individual (or private) water system |
A water system not owned or operated by a water utility and that
serves <15 residences or farms not having access to a public water
system.
|
| Maximum-contaminant level |
The maximum permissible concentration (i.e., level) of a contaminant
in water supplied to any user of a public water system.
|
| Nephelometric turbidity units |
The units in which the turbidity of a sample of water is measured when
the degree to which light is scattered is assessed with a
nephelometric turbidimeter.
|
| Noncommunity water system |
A public water system that 1) serves an
institution, industry, camp, park, hotel, or business that is used by
the public for >60 days/year, 2) has >15 service connections or serves
an average of >25 persons, and 3) is not a community water system. |
| Nontransient noncommunity water
systems |
Public water systems that
serve >25 of the same persons for >6 months/year (e.g., a factory or
school).
|
| Oocyst |
The infectious stage of
Cryptosporidium parvum and certain other coccidian parasites with
a protective wall that facilitates survival in water and other
environments. |
| Public water system |
A system, classified as either a community water system or a
noncommunity water system, that provides piped water to the public for
human consumption and is regulated under the Safe Drinking Water Act. |
| Raw water |
Surface water or groundwater that has not been treated in any way.
|
| Reverse osmosis |
A filtration process that removes dissolved salts and metallic ions
from water by forcing it through a semipermeable membrane. This
process is also highly effective in removing microbes from water. |
| Source water |
Untreated water (i.e., raw water) used to produce drinking water.
|
| Surface water |
The water in lakes, rivers, reservoirs,
and oceans. |
| Total coliforms |
Nonfecal and fecal coliforms that are detected by using a standard
test. Total coliforms are a group of closely related bacteria that are
usually free-living in the environment, but are also normally present
in water contaminated with human and animal feces. With certain
exceptions, they do not cause disease. Specifically, coliforms are
used as a screen for fecal contamination as well as to determine the
efficiency of treatment and the integrity of the water distribution
system. The presence of total coliforms in drinking water indicates
that the system is either fecally contaminated or vulnerable to fecal
contamination. |
| Transient non-community water
systems |
Public water systems that regularly serve >25 of the same persons for
>6 months/year (e.g., highway rest stations, restaurants, and parks
with their own public water systems).
|
| Turbidity |
The quality (e.g., of water) of having
suspended matter (e.g., clay, silt, or plankton) that results in loss
of clarity or transparency. |
| Untreated water |
Surface water or groundwater that has not been treated in any way
(also called raw water).
|
| Water quality indicator |
A microbial, chemical, or physical
parameter that indicates the potential risk for infectious diseases
associated with using the water for drinking, bathing, or recreational
purposes. The best indicator is one whose density or concentration
correlates best with health hazards associated with a type of hazard
or pollution. |
| Water utility |
A water provider that distributes drinking water to a community
through a network of pipes.
|
| Watershed |
An area from which water drains to a single point; in a natural basin,
the area contributing flow (i.e., water) to a place or point on a
stream.
|
| Watershed-control program |
A program to protect a watershed from
contamination or pollution.
|
