Water: Glossary of Definitions
Glossary of Definitions
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.
agent See etiologic agent.
aquifer A geologic formation or part of a formation (e.g., gravel, sand, or porous stone) that yields water to wells or springs.
backflow A hydraulic condition caused by a difference in water pressure that causes nonpotable water or other liquid to enter the potable water system by either backpressure or backsiphonage. See cross-connection.
backpressure A hydraulic condition that results when pressure from a customer's water system (e.g., potentially nonpotable water) is higher than pressure in the public water system, resulting in backflow of water into the public water system.
backsiphonage A hydraulic condition caused by negative or subatmospheric pressure within a water system, resulting in backflow.
biofilm Microbial cells that adhere to a surface through a matrix of primarily polysaccharide materials in which they are encapsulated. Biofilms can grow on piping and surfaces of water systems and can be difficult to remove. They offer protection to microbes from disinfectants (e.g., chlorine) in the water.
boil-water advisory A statement to the public advising that tap water must be boiled before drinking.
bottled water Commercially produced bottled water.
class A categorization given to waterborne disease and outbreaks (WBDOs) indicating to the strength of the epidemiologic and water-quality data implicating water as the source of the disease or outbreak (see Table 3).
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). Coliforms are mostly harmless bacteria that live in soil and water as well as the gut of humans and animals.
community water system A public water system that has at least 15 service connections used by year-round residents or that regularly serves at least 25-year-round residents. The system might be owned by a private or public entity providing water to a community, subdivision, or mobile home park.
cross-connection Any actual or potential connection between a drinking water supply and a possible source of contamination or pollution (i.e., nonpotable water). Under this condition, contaminated water might flow back into the drinking water system. See backflow.
deficiency An antecedent event or situation contributing to the occurrence of a waterborne disease or outbreak.
dermatitis Inflammation of the skin. In this report, the term dermatitis is used to denote a broad category of skin-related symptoms (e.g., folliculitis, cellulitis, chemical burns, or rash).
disinfection A treatment that kills microorganisms (e.g., bacteria, viruses, and protozoa); in water treatment, a chemical (commonly chlorine, chloramine, or ozone) or physical process (e.g., ultraviolet light) may be used.
disinfection by-products Chemicals formed in water by the reaction between organic matter and other waste products and disinfectants.
distribution system Water pipes, storage reservoirs, tanks, and other means used to deliver drinking water to consumers or to store finished water before delivery to a customer. In community water systems, the distribution system is under the jurisdiction of a water utility and ends at the water meter or at the customer's property line (if the system is not metered). In noncommunity and nonpublic individual water systems, the distribution system ends at the point where water enters the building or house. See plumbing.
etiologic agent The pathogen, chemical, or toxin causing a waterborne disease or outbreak. Infectious etiologic agents are bacteria, parasites, viruses, or fungi.
fecal coliforms Coliform bacteria that grow and ferment lactose to produce gas at 112.1°F (44.5°C) in <24 hours. These bacteria are associated with human and animal wastes, and their presence in water might be an indication of recent sewage or animal waste contamination.
filtration In water treatment, the process of passing water through one or more permeable membranes or media of small diameter (e.g., sand, anthracite, and diatomaceous earth) to remove suspended particles from the water. Filters might be effective in removing pathogens, depending on the type and operation.
finished water The water (e.g., drinking water) delivered to the distribution system after treatment, if any.
free chlorine The chlorine in water that is not combined with other constituents, therefore, serving as an effective disinfectant (also referred to as free available chlorine and residual chlorine).
ground water Water that is contained in interconnected pores in an aquifer.
ground water system A system that uses water extracted from an aquifer (i.e., a well or spring) as its source.
ground water under the direct influence of surface water As defined by the U.S. Environmental Protection Agency (EPA), 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 Cryptosporidium), or substantial and relatively rapid shifts in water characteristics (e.g., turbidity, temperature, conductivity, or pH) that closely correlate with climatologic or surface water conditions. Direct influence must be determined for individual sources in accordance with criteria established by the state.
individual water system A water system that does not meet the EPA definition for a public water system. The system might serve a single family or farm not having access to a public water system, or it might regularly serve as many as 24 persons or 14 connections. States are responsible for regulating these water systems.
karst aquifer An aquifer characterized by water-soluble limestone and similar rocks in which fractures or cracks have been widened by the dissolution of the carbonate rocks by ground water; the aquifer might contain sinkholes, tunnels, or even caves.
maximum contaminant level The maximum permissible concentration (i.e., level) of a contaminant in water supplied to any user of a public water system.
mixed-agent outbreak More than one type of etiologic agent is identified in clinical specimens from affected persons, and each etiologic agent is found in more than 5% of positive clinical specimens (e.g., an outbreak with Giardia spp. [parasites] and Salmonella spp. [bacteria] with each agent identified in >5% of stool specimens).
mixed-illness outbreak More than one type of illness is reported by more than 50% of patients in a single outbreak (e.g., a combination of gastroenteritis and dermatitis).
mixed-source outbreak More than one type of source water is implicated in the outbreak (e.g., a combination of ground water and surface water).
mixed-system outbreak More than one type of water system is implicated in the outbreak (e.g., a combination of noncommunity and individual water systems).
noncommunity water system A public water system that is not a community system; it does not serve year-round residents. There are two types: transient and nontransient noncommunity systems.
nontransient noncommunity water system A public water system that is not a community system and that regularly serves at least 25 of the same persons for more than 6 months per year but not year-round (e.g., a school, a factory, or a business with its own water supply).
plumbing Water pipes, storage reservoirs, tanks, and other means used to deliver drinking water to consumers inside buildings or houses or to store drinking water inside buildings or houses before consumption. In community water systems, the plumbing begins after the water utility's water meter or at the property line (if the distribution system is not metered). In noncommunity and nonpublic individual water systems, the plumbing begins at the point where water enters the building or house. See distribution system.
predominant illness The category of illness reported by at least 50% of ill respondents (e.g., gastroenteritis, dermatitis, or acute respiratory illness). When more than one illness category is reported for a single WBDO, they are listed together as predominant illnesses. These mixed illness WBDOs are analyzed separately from WBDOs with single illnesses.
primary water exposure For use in this report, a classification used for the source of contaminated water not intended for drinking or contaminated water of unknown intent.
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. Such a system must have at least 15 service connections or regularly serve at least 25 persons daily for at least 60 days per year.
raw water Surface water or ground water that has not been treated in any way.
reservoir, impoundment An artificially maintained lake, created for the collection and storage of water. This body of water can be available as a source of raw water for drinking purposes and/or recreational use. In certain instances, a finished water storage facility in the distribution system might also be called a reservoir.
setting Location where exposure to contaminated water occurred (e.g., restaurant, water park, or hotel).
source water Untreated water (i.e., raw water) used to produce drinking water.
surface water All water on the surface (e.g., lakes, rivers, reservoirs, ponds, and oceans) as distinguished from subsurface or ground water.
total coliforms Fecal and nonfecal coliforms that are detected by using a standard test. The extent to which total coliforms are present in water can indicate the general quality of that water and the likelihood that the water is fecally contaminated by animal and/or human sources.
transient noncommunity water system A public water system that is not a community system and that does not regularly serve at least 25 of the same persons for more than 6 months per year. These systems provide water to places where persons do not remain for long periods (e.g., restaurants, campgrounds, highway rest stations, or parks with their own public water systems).
untreated water Surface water or ground water that has not been treated in any way (i.e., raw water).
water not intended for drinking Water that has not been treated for human consumption in conformance with EPA drinking water standards and that is provided for uses other than for drinking. This might include water used in occupational settings; lakes, springs, and creeks used as drinking water by campers and boaters; irrigation water; and other nonpotable water sources with or without taps but does not include exposure to recreational water or flood water.
water of unknown intent The information about the water is insufficient to determine for what purpose it is being provided or used and whether is has been treated for human consumption in conformance with EPA drinking water standards.
water system A system for the provision of water for human consumption through pipes or other constructed conduits. This includes any collection, treatment, storage, and distribution facilities used primarily in connection with such a system.
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