Water Resources Glossary

Aquifer - a porous, water-bearing geologic formation.


Basin - land area where precipitation runs off into streams, rivers, lakes and reservoirs. It is a land feature that can be identified by tracing a line along the highest elevations (often a ridge) between two areas. Also called a watershed.


Bond rating - a numerical figure assigned by the N.C. Municipal Council to a local government’s capacity to assume debt. The rating is based on several indicators of financial health and stability, including budgetary soundness, tax base and demographics. Bond ratings less than 75 on a scale of 1-100 are assessed as more risky for investment. Local governments with those low ratings have limited, if any, access to the private market for financing. Because of the locality’s inability to repay, loans from public agencies also may be difficult to obtain.


Bulk water use - sale of a significant quantity of water to another system generally for the purpose of resale.


Capacity Use Area - designation by the state Environmental Management Commission of a geographic area where the aggregate use of groundwater or surface water exceeds or threatens to exceed the replenishment rate and thus requires coordination and/or limitations on use.


Capital improvement plan - a community plan for short- and/or long-term physical development.


Clean water infrastructure - sewer and stormwater systems.


Economically distressed - a term assigned to the lowest three tiers of North Carolina’s five-tier rankings for counties. The N.C. Department of Commerce assigns the tiers annually based on several economic indicators.


Floodplain - area adjacent to a river or stream subject to periodic flooding. The 100-year floodplain refers to an area likely to be flooded at least once in 100 years.


Geographic Information System - a computer hardware and software system that captures, analyzes and displays interrelated and geographically linked data.


Groundwater - subsurface water occupying the saturation zone, from which wells and springs are fed. The term applies only to water below the water table.


Headwater(s) - source and upper reaches of a stream; also the upper reaches of a reservoir.


High unit costs - utility improvements that, spread out over the customer base, would result in combined water and sewer utility rates exceeding 1.5 percent of median household income.


Inflow and infiltration (I&I) - the intrusion of groundwater and stormwater into sewer systems, usually through breaks, cracks or failed joints in sewer collection pipes.


Infrastructure (water, sewer, and stormwater) - the system of pipes, ditches, channels, etc. that carries water, sewage and stormwater through and under a city.


Maintenance - upkeep necessary for efficient operation of physical properties. It involves labor and materials, but is not to be confused with replacement or retirement.


Moratorium - an order imposed on utility owners to deny any additional water or sewer connections. Moratoria are most often issued to system owners that have serious, ongoing problems with their treatment capacity or collection systems, resulting in untreated or partially treated sewage being released into public waterways.


Operating expenses - expenses necessary for the maintenance, operation and collection of revenue for a specific utility. Some business expenses are excluded from the operating expense category for rate-making purposes if the expenses are not related to the provision of service.


Public sewer system - a system of lines that collects wastewater and transports it to a treatment facility. A system may include wastewater treatment and collection or collection only. Regional or interconnected utilities may count as more than one “system” if local governments retain ownership of individual portions.


Public water system - a drinking water system that serves at least 25 people or 15 service connections for at least 60 days per year. A system may include drinking water treatment and a distribution network or a distribution network only. Regional or interconnected utilities may count as more than one “system” if local governments retain ownership of individual portions.


Rate structures (water or sewer):

Increasing block rate
rates (or prices) applicable to blocks of usage (each 1,000 gallons, for example) in which the block rate increases
as consumption or use increases.
Seasonal uniform rate
rates charging the same amount per unit but with variation according to the season. Most often, this will refer to
a water system that charges more during high-demand summer months.
Uniform rate
a single rate per unit of volume that does not vary with quantity used so, for example, the first gallon is water is priced at the same rate as gallon 5,000.
Declining block rate
rates applicable to blocks of usage (each 1,000 gallons, for example) in which the rate charged decreases as consumption increases.
Flat fee
a fixed charge for service regardless of quantity of use.

Regionalization - adoption of water or sewer improvement projects that are regional in scope. These may range from cooperation by two neighboring towns to multi-county systems.


Rural - Counties with a population density of fewer than 200 people per square mile (1990 Census). Of North Carolina’s 100 counties, 85 are rural.


Septic system - an onsite treatment system for wastewater, most often belonging to an individual residence or business.


Sewage treatment technologies:

Activated sludge
biological treatment process in which a mixture of sewage and activated sludge (produced with the use of bacteria and other organisms) is agitated and aerated. The activated sludge is subsequently separated from the treated sewage by settlement and may be re-used.
Advanced secondary
treatment that begins at the end the secondary settling stage. Among its primary purposes is the removal of excess ammonia, which is toxic to aquatic life. Advanced secondary treatment employs technologies such as trickling filters.
Extented aeration
a process that introduces oxygen to wastewater, promoting the growth of aerobic bacteria to destroys organic compounds in the sewage. Incoming wastewater passes through three progressive stages of treatment before being discharged from the plant.
shallow ponds where sunlight, bacterial action and oxygen work to purify wastewater. Lagoons provide primary treatment for wastewater.
Nutrient removal
an additional step to remove pollutants such as phosphorous or nitrogen that can fuel abnormally high organic growth in aquatic ecosystems.
the second stage of wastewater treatment, which removes organic materials and nutrients. This is done with the help of bacteria. The wastewater flows to large, aerated tanks where bacteria consume as much of the solids and nutrients as possible. The remaining solids settle out to the bottom of the tank.
Septic system
an onsite treatment system for sewage involving use of an underground tank, where bacteria in the sewage decompose the organic wastes.
Spray irrigation
the process of collecting water from the top of lagoon ponds and spraying the water on a crop that can absorb (remove) the nutrients from the wastewater.
the third stage of treating sewage or effluents, by removing suspended solids and or pollutants. Typically, the third stage will use chemicals to remove phosphorous and nitrogen from the water, but may also include filter beds and other types of treatment. Chlorine added to the water kills any remaining bacteria. The water is then discharged.

Sewer system I&I correction activities:

Camera inspection
an inspection of sewer collection lines by a remote-controlled video camera.
Capital Improvement Plan (CIP)
a community plan for short- and/or long-term physical development.
Headworks analysis
a study that consists of an evaluation of the wastewater treatment plant’s capability to treat wastewater containing pollutants that can affect the plant’s performance if they are presented in the wasteflow in sufficient concentrations. It is generally conducted in connection with establishing a pretreatment program for local industries that discharge to the plant.
Smoke testing
a process through which smoke canisters are placed in isolated sewer collection lines to detect leaks in the system.
Line inspection and cleaning
regular inspection of sewer collection lines and cleaning of those lines to remove build-up that impedes the flow of wastewater.
Line rehabilitation and replacement
the rehabilitation of sewer collection lines through any of a variety of new technologies for the purpose of sealing the lines. Line replacement generally occurs when the line is too severely compromised to be rehabilitated.
Mapped in GIS (Geographic Information System)
maps integrated into multi-layered computerized databases. This allows the user to define traits for display and to link maps to related information, such as water or sewer system components.

Special Order by Consent - a contractual agreement generally between a sewer system operator or other permit holder and the State of North Carolina, represented by the Environmental Management Commission, to achieve stipulated actions to reduce, eliminate or prevent water quality degradation. Limits set for particular environmental standards may be relaxed under an SOC for the time determined reasonable to make the necessary improvements.


Surface Water - all the water visible on the surface, in rivers, lakes, ponds, creeks, estuaries, etc.


Stormwater - the portion of rainfall that runs off the property and does not soak into the ground.


Treated (finished) water - raw water obtained from supply sources and treated to produce potable (drinking-quality) water.


Urban - counties with a population density of 200 people per square mile or greater (1990 Census). Fifteen of North Carolina’s 100 counties are urban.


Water reuse and conservation - measures to reduce water use and/or effluent going into public waterways from wastewater treatment plants. Water conservation may be as simple as low-flow toilets and showerheads. Water reuse, or recyling, typically involves reusing partially treated wastewater for beneficial purposes, such as irrigation, industrial processes or toilet flushing.


Water system water loss correction activities:

Leak detection program
a program whereby one of a number of technologies is employed to determine where leaks exist in water distribution lines.
Valve exercise program
a process whereby water valves are regularly checked to determine that they are properly functioning and capable of being opened and closed.
Meter replacement program
a program whereby water meters are replaced or recalibrated on a regular schedule so that water is appropriately metered.
Leak detection study
a search for leaks in the system, usually done when the percentage of unaccounted for water is high.

Wastewater - water that has been used in homes, industries, and businesses that is not for reuse unless it is treated.


Water budget - calculation of the inflow, outflow, and storage of groundwater and surface water for a basin or water resources unit to determine the availability of water.


Water table - the upper surface of the zone of saturation closest to the ground surface.