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Drinking Water Mapping Application to Protect Source Waters (DWMAPS) Glossary

This page provides definitions of terms used in the Drinking Water Mapping Application to Protect Source Waters (DWMAPS), organized both by tool and alphabetically.

On this page:

Drinking Water Providers

Area Served: Name of the administrative jurisdiction receiving drinking water from a public water system. A public water system may serve multiple jurisdictions.

Groundwater: The supply of fresh water found beneath the Earth's surface, usually in aquifers, which supply wells and springs

Health-Based Violation:  A type of violation of the Safe Drinking Water Act incurred by a public water system. These violations fall into three categories: 1) exceedances of the maximum contaminant levels (MCLs) which specify the highest allowable contaminant concentrations in drinking water, 2) exceedances of the maximum residual disinfectant levels (MRDLs), which specify the highest concentrations of disinfectants allowed in drinking water, and 3) treatment technique requirements, which specify certain processes intended to reduce the level of a contaminant.

HUC12 (Hydrologic Unit Code 12): Subdivisions within a watershed. Subwatersheds are the sixth level (12-digit) of the hydrologic unit hierarchy. For more information, see Hydrologic Unit Maps.

Non-Transient, Non-Community Water System (NTNCWS): 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.

Public Water System (PWS) (Drinking Water Provider): Any water system which provides water to the public for consumption, serving at least an average of 25 individuals for at least 60 days annually, or at least 15 service connections. There are more than 170,000 PWSs providing water from wells, rivers, or other sources to about 250 million Americans. Private wells provide water to the remaining population.

Population Served: The population amount served by a public water system.

Source (Drinking Water Source; Source Type): A source of water for a drinking water system. Includes: Intake, Well, Reservoir, or Spring

Source Water: Water in its natural state, prior to any treatment for drinking.

Surface Water: All water natural open to the atmosphere, such as rivers, lakes, and reservoirs

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.

Watershed: The land area from which water drains into a stream, river, or reservoir.


Potential Sources of Contamination

Contaminant: Anything found in water (including microorganisms, minerals, chemicals, radionuclides, etc.) which may be harmful to human health. DWMAPS includes contaminants for which a public water system may incur a violation of a national primary drinking water regulation.

Discharge: Any emission (other than natural seepage), intentional or unintentional. Includes, but is not limited to, spilling, leaking, pumping, pouring, emitting, emptying or dumping.

HUC12 (Hydrologic Unit Code 12): Subdivisions within a watershed. Subwatersheds are the sixth level (12-digit) of the hydrologic unit hierarchy. For more information, see Hydrologic Unit Maps.

Load: The total amount of pollutants entering a waterbody from one or multiple sources, measured as a rate, as in weight per unit time or per unit area.

National Pollution Discharge Elimination System (NPDES): A national program under Section 402 of the Clean Water Act for regulation of discharges of pollutants from point sources to waters of the United States. Discharges are illegal unless authorized by an NPDES permit, which sets specific limits on the type and amount of pollutants that a municipality or industry can discharge to a receiving water, and a compliance schedule for achieving those limits.

NPDES Facility ID (NPDES Permit Number): National Pollution Discharge Elimination System (NPDES) permit identification number.

Permitted Discharge Facility: Facility permitted to discharge wastewater directly to surface water under the National Pollution Discharge Elimination System (NPDES).

Point Source Discharger (Direct Discharger): A point source that discharges a pollutant(s) to waters of the United States, such as streams, lakes, or oceans. These sources are subject to the National Pollutant Discharge Elimination System program regulations. Municipal and industrial facilities that introduce pollution through a defined conveyance or system such as outlet pipes are direct dischargers.

Point Source Pollution (Point Source Discharge): Pollutant loads discharged at a specific location from pipes, outfalls, and conveyance channels from either municipal wastewater treatment plants or industrial waste treatment facilities. Point sources can also include pollutant loads contributed by tributaries to the main receiving water stream or river.

Potential Sources of Contamination (PSC): A facility (a site known to hold or discharge a contaminant) or event (such runoff or a combined sewer overflow) which could pose a potential source of contamination to drinking water supplies.

Surface Water: All water natural open to the atmosphere, such as rivers, lakes, and reservoirs. 


Nearby Discharges

Contaminant: Anything found in water (including microorganisms, minerals, chemicals, radionuclides, etc.) which may be harmful to human health. DWMAPS includes contaminants for which a public water system may incur a violation of a national primary drinking water regulation.

Discharge: Any emission (other than natural seepage), intentional or unintentional. Includes, but is not limited to, spilling, leaking, pumping, pouring, emitting, emptying or dumping.

HUC12 (Hydrologic Unit Code 12): Subdivisions within a watershed. Subwatersheds are the sixth level (12-digit) of the hydrologic unit hierarchy. For more information, see Hydrologic Unit Maps.

Load: The total amount of pollutants entering a waterbody from one or multiple sources, measured as a rate, as in weight per unit time or per unit area.

National Pollution Discharge Elimination System (NPDES): A national program under Section 402 of the Clean Water Act for regulation of discharges of pollutants from point sources to waters of the United States. Discharges are illegal unless authorized by an NPDES permit, which sets specific limits on the type and amount of pollutants that a municipality or industry can discharge to a receiving water, and a compliance schedule for achieving those limits.

NPDES Facility ID (NPDES Permit Number): National Pollution Discharge Elimination System (NPDES) permit identification number.

Permitted Discharge Facility: Facility permitted to discharge wastewater directly to surface water under the National Pollution Discharge Elimination System (NPDES).

Point Source Discharger (Direct Discharger): A point source that discharges a pollutant(s) to waters of the United States, such as streams, lakes, or oceans. These sources are subject to the National Pollutant Discharge Elimination System program regulations. Municipal and industrial facilities that introduce pollution through a defined conveyance or system such as outlet pipes are direct dischargers.

Point Source Pollution (Point Source Discharge): Pollutant loads discharged at a specific location from pipes, outfalls, and conveyance channels from either municipal wastewater treatment plants or industrial waste treatment facilities. Point sources can also include pollutant loads contributed by tributaries to the main receiving water stream or river

Surface Water: All water natural open to the atmosphere, such as rivers, lakes, and reservoirs. 


Polluted Waterways

Impaired Waters (Impairments; 303(d)): Waters with chronic or recurring monitored violations of the applicable numeric or narrative water quality standards under the Clean Water Act (see CWA SECTION 303(d)). States are required to develop lists of impaired waters and set priority rankings for the waters on the list and develop Total Maximum Daily Loads (TMDLs) for those waters.

Total Maximum Daily Load (TMDL): Defines the pollutant load that a water body can acquire without violating water quality standards, and allocates the pollutant loading between contributing point sources and non-point sources.

HUC12 (Hydrologic Unit Code 12): Subdivisions within a watershed. Subwatersheds are the sixth level (12-digit) of the hydrologic unit hierarchy. For more information, see Hydrologic Unit Maps.

Reach Code: A unique 14-digit identification code assigned to a National Hydrography Dataset reach, which is a continuous piece of surface water with similar hydrologic characteristics. The first eight digits are the HUC for the sub-basin in which the reach exists, and the last six digits are a sequential number that is assigned when reach codes are allocated in the sub-basin.


Projects and Source Water Collaboratives

Section 319: Section of the Clean Water Act under which EPA has developed guidelines to help states, territories, and tribes implement nonpoint source pollutant management programs and provide grants to fund the programs.

319 Nonpoint Source Project: Nonpoint source pollution reduction project funded under the Clean Water Act Section 319 Nonpoint Source Management Program. Under Section 319, states, territories and tribes receive grant money that supports a wide variety of activities including technical assistance, financial assistance, education, training, technology transfer, demonstration projects and monitoring to assess the success of specific nonpoint source implementation projects.

319 Project ID: Clean Water Act Section 319 Nonpoint Source Management Program grant project identification number.

HUC12 (Hydrologic Unit Code 12): Subdivisions within a watershed. Subwatersheds are the sixth level (12-digit) of the hydrologic unit hierarchy. For more information, see Hydrologic Unit Maps.

Source Water Collaborative: A non-profit partnership, organization, or coalition established to support source water protection.


All Definitions

303(d): Refers to section 303(d) of the Clean Water Act, which requires states, territories, and authorized tribes to develop lists of impaired waters every two years (i.e., Section 303(d) list). The states identify all waters where required pollution controls are not sufficient to attain or maintain applicable water quality standards. States are required to establish priorities for development of TMDLs for waters on the 303(d) list.

305(b): Refers to section 305 subsection (b) of the Clean Water Act. 305(b) generally describes a report of each states water quality, and is the principle means by which EPA, Congress, and the public evaluate whether US waters meet water quality standards, the progress made in maintaining and restoring water quality, and the extent of the remaining problems.

319 Nonpoint Source Project: Nonpoint source pollution reduction project funded under the Clean Water Act Section 319 Nonpoint Source Management Program. Under Section 319, states, territories and tribes receive grant money that supports a wide variety of activities including technical assistance, financial assistance, education, training, technology transfer, demonstration projects and monitoring to assess the success of specific nonpoint source implementation projects

319 Project ID: Clean Water Act Section 319 Nonpoint Source Management Program grant project identification number.

Aquifer Exemption: An aquifer is an underground body of rock that contains or can transmit groundwater. Underground Injection Control regulations allow EPA to exempt aquifers that do not currently serve as a source of drinking water and will not serve as a source of drinking water in the future, based on certain criteria.

Area Served: Name of the administrative jurisdiction receiving drinking water from a public water system. A public water system may serve multiple jurisdictions.

Assessed (305b): Under Section 305(b) of the CWA, the states, territories, and other jurisdictions of the United States are required to submit reports on the quality of their waters to the U.S. Environmental Protection Agency (EPA) every 2 years. From the assessment a list of impaired waters is developed - the 303(d) list. During the assessment, water body condition is evaluated for seven designated beneficial uses (such as aquatic life habitat, drinking water supply, fish consumption, and water contact recreation). If water quality in an assessed water body has been degraded and does not meet the standards for beneficial uses, the water body may be designated as impaired or threatened, depending on the severity of the degradation.

Brownfields (ACRES): A brownfield is an abandoned, idled, or underused industrial and commercial facility/site where expansion or redevelopment is complicated by real or perceived environmental contamination. EPA's Brownfields initiative helps communities mitigate potential health risks and restore the economic viability of such areas or properties

Catchment (Watershed): The incremental drainage area for a linear hydrologic feature found in the National Hydrography Dataset (NHD).

CERCLA (Comprehensive Environmental Response, Compensation, and Liability Act): The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund, was enacted by Congress on December 11, 1980. This law created a tax on the chemical and petroleum industries and provided broad Federal authority to respond directly to releases or threatened releases of hazardous substances that may endanger public health or the environment. DWMAPS includes sites on the National Priority List (see National Priority List).

Contaminant: Anything found in water (including microorganisms, minerals, chemicals, radionuclides, etc.) which may be harmful to human health. DWMAPS includes contaminants for which a public water system may incur a violation of a national primary drinking water regulation.

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA): The Federal Insecticide, Fungicide, and Rodenticide Act was enacted in June 25, 1947. The Act instructs the EPA to regulate: 1) the registration of all pesticides used in the United States, 2) the licensing of pesticide applicators, 3) re-registration of all pesticide products, 4) the storage, transportation, disposal and recall of all pesticide products.

Freight Network: The U.S. Rail Network Nationwide Freight Rail System. The freight network shows all privately owned freight rail lines.

Groundwater The supply of fresh water found beneath the Earth's surface, usually in aquifers, which supply wells and springs.

Hazmat Route: State-assigned hazardous material routes from the National Transportation Atlas Database (NTAD).

Health-Based Violation:  A type of violation of the Safe Drinking Water Act incurred by a public water system. These violations fall into three categories: 1) exceedances of the maximum contaminant levels (MCLs) which specify the highest allowable contaminant concentrations in drinking water, 2) exceedances of the maximum residual disinfectant levels (MRDLs), which specify the highest concentrations of disinfectants allowed in drinking water, and 3) treatment technique requirements, which specify certain processes intended to reduce the level of a contaminant.

HUC12 (Hydrologic Unit Code 12): Subdivisions within a watershed. Subwatersheds are the sixth level (12-digit) of the hydrologic unit hierarchy. For more information, see Hydrologic Unit Maps.

Impaired Waters (Impairments; 303(d)): Waters with chronic or recurring monitored violations of the applicable numeric or narrative water quality standards under the Clean Water Act (see CWA SECTION 303(d)). States are required to develop lists of impaired waters and set priority rankings for the waters on the list and develop Total Maximum Daily Loads (TMDLs) for those waters.

Inventory: The count of public water system facilities serving a specific geographic area.

Land Cover: Anything that is visible from above the Earth's surface. Examples include vegetation, exposed or barren land, water, snow, and ice. Layer title refers to the National Land Cover Database (2011) created by the Multi-Resolution Land Characteristics Consortium.

Landfill: Waste processing and disposal operation.

Load: The total amount of pollutants entering a waterbody from one or multiple sources, measured as a rate, as in weight per unit time or per unit area.

Maximum Contaminant Level (MCL): The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to Maximum Contaminant Goals (MCLGs) as feasible, considering costs and technology. MCLs are enforceable standards under the Safe Drinking Water Act.

Maximum Contaminant Goals (MCLGs): The maximum level of a contaminant that is associated with no adverse health effects from drinking water containing that contaminant over a lifetime. For chemicals believed to cause cancer, the MCLGs are set at zero. MCLGs are not enforceable, but are ideal, health-based goals which are set in the National Primary Drinking Water Standards developed by EPA. MCLs are set as close to MCLGs as possible, considering costs and technology.

National Hydrography Dataset (NHD): The NHD represents the surface water drainage network with features such as rivers, streams, canals, lakes, ponds, coastline, dams, and stream gages.

National Pollution Discharge Elimination System (NPDES): A national program under Section 402 of the Clean Water Act for regulation of discharges of pollutants from point sources to waters of the United States. Discharges are illegal unless authorized by an NPDES permit, which sets specific limits on the type and amount of pollutants that a municipality or industry can discharge to a receiving water, and a compliance schedule for achieving those limits.

NPDES Facility ID: National Pollution Discharge Elimination System (NPDES)--permitted facility identification number.

National Primary Drinking Water Regulation (NPDWR): A legally-enforceable standard that applies to public water systems; protects drinking water quality by limiting the levels of specific contaminants that can adversely affect public health and are known or anticipated to occur in water from public water systems; and takes the form of maximum contaminant level or treatment technique rules

National Priorities List: A Federal roster of uncontrolled contamination sites that actually, or potentially, threaten human health or the environment and are eligible for extensive, long-term investigation and cleanup under CERCLA, the Federal Superfund program.

Nonpoint Source Pollution: Pollution that is not released through pipes but rather originates from multiple sources over a relatively large area. Nonpoint sources can be divided into source activities related either to land or water use including failing septic tanks, improper animal-keeping practices, forestry practices, and urban and rural runoff.

Non-Transient, Non-Community Water System (NTNCWS): 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 solvents and pesticides, which can get into water through runoff from cropland or discharge from factories. As of the 2012 definition, EPA has set legal limits on 56 organic contaminants.

Passenger Network: The U.S. Rail Network Nationwide passenger rail system.

Permitted Discharge Facility: Facility permitted to discharge wastewater directly to surface water under the National Pollution Discharge Elimination System (NPDES).

Percent Watershed Natural Land Cover: Dataset represents the percent of total land within each subwatershed (12-digit HUC) that has natural land cover for 2011. Natural land cover includes forests, shrubs, grasslands, barren land, and wetlands; it excludes agriculture and impervious surfaces.

Percent Watershed Impervious Area: Dataset represents the percent of total land within each subwatershed (12-digit HUC) that is impervious for 2011. Impervious surfaces do not allow the penetration of water and include buildings, roads, and sidewalks. 

Point Source Discharger (or Direct Discharger): A point source that discharges a pollutant(s) to waters of the United States, such as streams, lakes, or oceans. These sources are subject to the National Pollutant Discharge Elimination System program regulations. Municipal and industrial facilities that introduce pollution through a defined conveyance or system such as outlet pipes are direct dischargers.

Point Source Pollution (or Point Source Discharge): Pollutant loads discharged at a specific location from pipes, outfalls, and conveyance channels from either municipal wastewater treatment plants or industrial waste treatment facilities. Point sources can also include pollutant loads contributed by tributaries to the main receiving water stream or river.

Population Served: The population amount served by a public water system.

Potential Sources of Contamination (PSC): A facility (a site known to hold or discharge a contaminant) or event (such runoff or a combined sewer overflow) which could pose a potential source of contamination to drinking water supplies.

Protected Areas: Refers to the Protected Areas Database (PAD-US), a national inventory of U.S. terrestrial and marine protected areas that are dedicated to the preservation of biological diversity and to other natural, recreation and cultural uses, managed for these purposes through legal or other effective means. Lands in PAD-US are mainly open space/resource lands owned in fee by agencies and non-profits. Conservation easements suitable for distribution in the public domain are also included. The PAD-US database is created and maintained by the United States Geological Survey Gap Analysis Program. Learn More at: https://gapanalysis.usgs.gov/padus/data/

Reach Code: A unique 14-digit identification code assigned to a National Hydrography Dataset reach, which is a continuous piece of surface water with similar hydrologic characteristics. The first eight digits are the HUC for the sub-basin in which the reach exists, and the last six digits are a sequential number that is assigned when reach codes are allocated in the sub-basin

Resource Conservation and Recovery Act (RCRA):  The public law that creates the framework for the proper management of hazardous and non-hazardous solid waste.

Source Water Protection Area: The area delineated by a state for a Public Water Supply or including numerous such suppliers, whether the source is ground water or surface water or both.

Public Water System (PWS): Any water system which provides water to the public for consumption, serving at least an average of 25 individuals for at least 60 days annually, or at least 15 service connections. There are more than 170,000 PWSs providing water from wells, rivers, or other sources to about 250 million Americans. Private wells provide water to the remaining population.

Regulated Contaminant: Contaminants in drinking water whose levels are limited by the National Primary Drinking Water Regulations (NPDWRs or primary standards). The NPDWRs are legally enforceable standards that apply to public water systems, to protect public health.

Risk Type: A facility (a site known to hold or discharge a contaminant) or event (such as a combined sewer overflow) which could pose a potential source of contamination to drinking water supplies.

Section 319: Section of the Clean Water Act under which EPA has developed guidelines to help states, territories, and tribes implement nonpoint source pollutant management programs and provide grants to fund the programs

Source (Drinking Water Source; Source Type): A source of water for a drinking water system. Includes: Intake, Well, Reservoir, or Spring

Source Water: Water in its natural state, prior to any treatment for drinking

Source Water Collaborative: A non-profit partnership, organization, or coalition established to support source water protection.

Superfund: The common name for the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Superfund refers to the entire CERCLA program as well as the trust fund established to fund cleanup of contaminated sites where potentially responsible parties cannot be identified, or are unwilling or unable to pay.

Surface Water: All water natural open to the atmosphere, such as rivers, lakes, and reservoirs.

System Type: A code value which classifies the type of public water system according to federal and state requirements. See: community water system (CWS), non-transient non-community system (NTNCWS), and transient non-community system (TNCWS).

Total Maximum Daily Load (TMDL): Defines the pollutant load that a water body can acquire without violating water quality standards, and allocates the pollutant loading between contributing point sources and non-point sources.

Toxic Release Inventory: A database of annual toxic releases from certain manufacturers compiled from EPCRA Section 313 reports. Manufacturers must report annually to EPA and the states the amounts of almost 350 toxic chemicals and 22 chemical categories that they release directly to air, water, or land, inject underground, or transfer to off-site facilities. EPA compiles these reports and makes the information available to the public under the "Community Right-to-Know" portion of the law.

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.

Toxic Substances Control Act (TSCA): The Toxic Substances Control Act (TSCA) of 1976 was enacted by Congress to give EPA the ability to track the 75,000 industrial chemicals currently produced or imported into the United States. TSCA inventory refers to the inventory of chemicals produced pursuant to Section 8 (b) of the Toxic Substances Control Act.

Underground Storage Tanks (UST): A tank and any underground piping connected to the tank that has 10% or more of its volume (including pipe volume) beneath the surface of the ground. USTs are designed to hold gasoline, other petroleum products, and hazardous materials.

Violation: A failure to meet requirements of any state or federal regulation. In DWMAPS this refers to a specific violation of a primary drinking water regulation incurred by a public water system.

Wastewater: Water carrying wastes from homes, businesses and industries that is a mixture of water and dissolved or suspended solids.

Wastewater Treatment Plant (WWTP): A facility containing a series of tanks, screens, filters, and other processes by which pollutants are removed from water. Most treatments include chlorination to attain safe drinking water standards. DWMAPS points represent NPDES permitted discharge points to receiving waters.

Water Quality: The biological, chemical, and physical conditions of a waterbody. It is a measure of a water body’s ability to support beneficial uses.

Water Source: The primary source of water for the water system. Includes: Intake, Well, Reservoir, or Spring

Watershed: The land area from which water drains into a stream, river, or reservoir.

Watershed Boundary Dataset: The Watershed Boundary Dataset (WBD) defines the areal extent of surface water drainage to a point, accounting for all land and surface areas. The WBD represents surface water drainage basins as enclosed areas in eight different size categories: Hydrologic Unit Code (HUC) 2—Hydrologic Unit Code 16.