Water Terms Glossary

We depend upon water for our very existence. The impact of water quality and quantity issues has never been greater. Yet the terminology used to describe the water we drink, the water we provide to plants and animals, the water stored underground, in lakes, rivers, and oceans, is not well understood by many.

This listing of water-related terms is intended to reduce the potential for misunderstanding presentations made by elected officials, environmental agencies, and news reporters. The definitions and associated explanations provide a working knowledge of water. Some terminology could be defined differently to describe water supply issues in other locations in the world.


Absorption is the process by which chemicals in gaseous, liquid, or solid phases are incorporated into and included within another gas, liquid, or solid chemical. For example, sponges absorb water.

Acceptable daily intake (ADI) is the chemical ingestion level determined by combining the maximum No-Observed-Adverse-Effect-Level (NOAEL) over a day of a particular chemical minus an uncertainty (safety) factor. Chemicals with ADI levels usually are not considered or suspected to be carcinogens. This classification results from toxicity data collected during prolonged ingestion studies conducted on a number of animals.

Acidity - The base-neutralizing capacity of a water is known as acidity. Acids contribute to corrosiveness and influence chemical reactions and chemical/biological processes.

Acre-foot is the volume of water (325,851 gallons of water) required to cover one acre of land with 12 inches of water.

Adsorption is the adherence of gas molecules, ions or solutions to the surface of solids. For example, odors from freezers and refrigerators are adsorbed to baking soda: dissolved cations adsorb onto the surface of ion-exchange resins.

Advection is the process by which chemicals and heat are transported along with the bulk motion of flowing gas or liquid. For example, nitrates move through soils and aquifer formations due predominantly to the bulk motion or movement of water. Advection usually refers to the horizontal movement of a gas or liquid; vertical movement would be convection.

Alkalinity - The acid neutralizing capacity of a water is known as alkalinity. For surface waters, alkalinity has been called "The Protector of the Stream", since the alkalinity of the water resists sudden changes in the pH of the stream associated with the influx of acid deposition, water containing organic acids, acidic groundwater discharges, or acidic industrial wastes.

Most surface waters have alkalinity’s < 200 mg CaCO3/L, but in limestone areas the alkalinity can be greater than 1000 mg CaCO3/L. In some cases, pristine surface waters have very low alkalinity and therefore they would be adversely impacted by acid mine drainage and acid rain. The alkalinity of precipitation can be from 1 to about 10 mg CaCO3/L. Absolutely pure water has no alkalinity whatsoever and becomes slightly acidic when CO2 from the air dissolves in the water to form carbonic acid.  Typically the best alkalinity for aquatic life is between 100 and 120 mg CaCO3/L. Alkalinity is determined by adding an acid, drop by drop (titration), to see how much acid it would take to cause the pH to start dropping.

Aluminum(Al): There is no published Maximum Contaminant Level (MCL), but 0.2 mg/L is considered safe. Elevated aluminum is believed to be associated with forms of dementia, such as Alzheimer’s.

Ammonia (NH4) -There is no MCL established for ammonia. Ammonia, however, is very toxic to fish and aquatic life. Ammonia concentrations of 0.06 mg/L can cause gill damage in fish and 0.2 mg/L is lethal to trout. Ammonia from the cat urine in kitty litter can kill bushes; don’t dump your used kitty litter near a plant you value. Concentrations in excess of 0.1 mg/L suggest domestic or agricultural sources of waste.

Anion is a negatively-charged ion. Nitrite (NO₂⁻) and chloride (Cl⁻) are examples of anions.

Anion exchange is the chemical process whereby negative ions of one chemical are preferentially replaced by negative ions of another chemical. In water treatment, the net effect is the removal of an unwanted ion from a water supply. For example, some municipalities are installing anion exchange systems to remove nitrate from their water supplies.

Anode - An anode is part of an electrochemical cell. The anode is the portion of the cell that the negatively charged electrons leave the system. The anode has a net positive charge and attracts negative charges. In solutions, anodes tend to attract anions. (also see Cathode)

Anode, Sacrificial - The use of a sacrificial anode is a form of catholic protection systems where the system is designed so the sacrificial anode corrodes to slow the corrosion of the more critical metal. In these system, the anode is made from a metal with a more negative electrochemical potential than the portion of metal component being protected. The difference in potential between the two metals means the sacrificial anode material corrodes in preference to the other component of the system that is more critical.

Antimony (Sb): The maximum contaminant level is 0.006 mg/L. Elevated levels of antimony can increase blood cholesterol and decrease blood glucose.

Aquifer is the saturated underground formation that will yield usable amounts of water to a well or spring. The formation could be sand, gravel, limestone, or sandstone. The water in an aquifer is called groundwater. A saturated formation that will not yield water in usable quantities is called an aquiclude. Most Pennsylvania aquifers may be categorized as confined or unconfined aquifers.

Confined Aquifer (artesian aquifer) is the saturated formation between low permeability layers that restrict movement of water vertically into or out of the saturated formation. Water is confined under pressure similar to water in a pipeline. Drilling a well into this type of aquifer is analogous to puncturing a pressurized pipeline. In some areas confined aquifers produce water without pumps (flowing artesian well). When pumping from confined aquifers, water levels often change rapidly over large areas. However, water levels will generally recover to normal when pumping ceases.

Unconfined Aquifer (water table aquifer) is the saturated formation in which the upper surface of the groundwater fluctuates with the addition or subtraction of water. The upper surface of an unconfined aquifer is called the water table. Water, contained in an unconfined aquifer, is free to move laterally in response to differences in the water table elevations.

Arsenic (As): The MCL for arsenic is 0.01 mg/L. Arsenic is highly toxic and its prevalence is due to the natural occurrence of this element in minerals and past use of arsenic in pesticides. Arsenic poisoning typically makes people feel tired and depressed and this poisoning is also associated with weight loss, nausea, and hair loss; it also causes white lines across your toenails and fingernails. For freshwater the concentration should be less than 0.01 mg/L.

Artificial Recharge is the unnatural (but not necessarily bad) addition of surface waters to groundwater. Recharge could result from reservoirs, storage basins, leaky canals, direct injection of water into an aquifer, or by spreading water over a large land surface.


Barium (Ba): The MCL is 2 mg/L. Barium can increase blood pressure.

Beryllium (Be): The MCL is 0.004 mg/L and it can cause intestinal lesions.

Baseflow is that part of streamflow derived from groundwater flowing into a stream. It usually makes up most of the flow of a stream most of the time.

Biological Oxygen Demand (BOD): Dissolved organic matter and some compounds in water will react with and remove dissolved oxygen in the water (the oxygen demand). One way to determine the oxygen demand of a particular water sample is to add microbes to the water and incubate the water, usually for five days, at 20 °C to see how much oxygen the microbes will use to oxidize the organic matter in the water – this is the biological oxygen demand, BOD. BOD is typically reported as 5-day BOD at 20 °C and reported as milligrams of oxygen consumed per liter (mg O/L). BOD 5 is used by regulatory agencies for monitoring wastewater treatment facilities and monitoring surface water quality. A sample with a 5-day BOD between 1 and 2 mg O/L indicates a very clean water, 3.0 to 5.0 mg O/L indicates a moderately clean water and > 5 mg O/L indicates a nearby pollution source. BOD is a laboratory test that requires an oxygen sensing meter, an incubator, nitrifying inhibitors, and a source of bacteria.


Cadmium (Cd): The MCL for cadmium is 0.01 mg/L. Cadmium poisoning is associated with kidney disease and hypertension and possibly mutations. For freshwater the concentration should be less than 0.0004 mg/L.

Calcium (Ca): No specific recommendation, but high calcium is associated with hardness, total dissolved solids problems and can cause aesthetic problems.

Cathode - A cathode is part of an electrochemical cell. The cathode is the portion of the cell that the negatively charged electrons enter the system. The cathode has a net negative charge and attracts positive charges. In solutions, cathodes tend to attract cations. (also see Anode)

Capillary fringe is a zone of partially saturated ground just above the water table. The depth of the fringe depends upon the size and distribution of the pore spaces within the geologic formation.

Carcinogenicity - A chemical complex or agent that will cause cancer in humans or animals that can be natural or man-made.

Class A - Pollutant that has adequate human data that indicates the chemical causes cancer in humans. (Human carcinogen)

Class B - Pollutant that has some human data (Group B1)  but sufficient animal data (Group B2) that suggests the chemical could cause cancer in humans. (Probable human carcinogen)

Class C - A possible human carcinogen, but has limited animal data and no or very little human data to support this hypothesis. (Possible human carcinogen)

Class D - Not classifiable as a human carcinogen because there is inadequate data to support that the chemical is or is not carcinogenic. (Not classifiable as a human carcinogen)

Class E - No evidence the chemical causes carcinogenic effects in animal studies. (Evidence of non-carcinogenicty for humans based on available data)

Cation is a positively charged ion. For example, calcium (Ca+2), and magnesium (Mg+2) are cations.

Cation exchange is a process whereby positively charged ions of one chemical are preferentially replaced by positive ions of another chemical. For example, water softeners replace Ca+2, and Mg+2 ions with the sodium (Na+) ion. Because the sodium ion has only one positive charge compared to the two of calcium and magnesium, the calcium and magnesium are more strongly attracted to the negative charges on the exchange resin.

Chloride (Cl): It is one of the major anions found in water and wastewater. The recommended maximum contaminant level is 250 mg/L, since the chloride ion imparts a funny taste to the water at that level (although it doesn’t really taste salty at that concentration. If ions of Calcium and Magnesium are present, the chloride ion may not impart a salty taste until over 1000 mg/L. In addition to human and animal waste, sources of chloride can include natural geological formations, road salt storage and applications, oil / natural gas drilling, and saltwater intrusions. High levels of chloride can attack and weaken metallic piping and fixtures and inhibit the growth of vegetation.

Chlorine: Chlorine, in one of a number of compounds, is added to water to destroy or deactivate disease-causing microorganisms and is the mostly widely used disinfectant in the United States. Elevated chlorine levels can create aesthetic problems (strong taste and odor) and if organic matter is present it can result in the creation of trihalomethanes, which are potentially carcinogenic, leading to liver and kidney cancer.

Chemical Oxygen Demand (COD): Dissolved organic matter and some compounds in water will react with and remove dissolved oxygen in the water (the oxygen demand). One way to determine the oxygen demand of a particular water sample is to add a strong oxidizing chemical to the water to see how much of the oxidizer will be used up to oxidize the dissolved organic matter in the water although it will include only the organic matter that is susceptible to oxidation by the strong chemical oxidant (the microbes used in determining biological oxygen demand can oxidize more organic matter because they have enzymes, ideal conditions, and five days to do it; determining COD is much faster than determining BOD). COD is typically used when there are industrial wastewater sources or incomparing biological to chemical oxidation in the selection of treatment process and performances Depending on the waste stream, COD can provide insight into the concentration of reduced inorganic metals in the water, such as ferrous iron, sulfide, and manganese.

Chromium (Cr): The MCL is 0.05 mg/L. The impact of chromium is not clearly defined, but it is known to adversely affect aquatic organisms.

Conductivity: The theoretical definition of conductivity is the "reciprocal of the resistance of a cube of a substance 1 cm on a side at a specified temperature". Typically the units of measure are micro-ohms/cm (µohms/cm) or microsiemens/cm (µS/cm). Conductivity or specific conductance is a measure of the ability of a fluid to carry a charge which is directly related to the concentration of dissolved substances. As the total dissolved substances in the water increases, the conductivity of the water also increases. For More information see Total Dissolved Solids.

Cone of depression is a depression in groundwater levels around a well in response to groundwater withdrawal (pumping water out of the well).

Contaminant is any undesirable biological, chemical, physical, or radiological substance or matter contained in water. As an example, trichloroethylene (TCE) is a synthetic cleaning solvent sometimes found in groundwater near manufacturing sites.

Copper (Cu): The MCL is 1 mg/L (Aesthetic) and 1.3 mg/L (Health-Based) . At 1 mg/L, the water may taste bitter and is highly toxic and may disrupt the metabolic processes, especially for children. For freshwater the concentration should be less than 0.036 mg/L.

Deep percolation is the movement of water below the maximum effective plant root zone. Percolation is the natural vertical movement of water in the ground.

Denitrifying Bacteria: In the process of denitrification of wastewater, the two key bacteria of ecological importance are Nitrosomonas and Nitrobacter. These bacteria facilitate or "catalyze" the reactions. Nitrosomonas results in the removal of three pairs of electrons from ammonia, facilitating the formation of nitrite and Nitrobacter removes two electrons from nitrite to form nitrate. The bacteria responsible for denitrification are autotrophic (make their own food) and heterotrophic (get food from others) facultative (they can manage in multiple environments) anaerobes (they thrive in no-oxygen environments). Monitoring for denitrifying bacteria is typically done to monitor the performance of denitrification systems.

Diffusion is a process whereby heat or chemicals are transported in response to differences in chemical concentration or temperature. Movement is from high concentration (or temperature) to low concentration (or temperature). This process could involve liquids, gases, and solids.

Discharge area is an area where groundwater moves toward or is delivered to the soil surface. Groundwater can flow into springs, or seeps; contribute baseflow to streams; or provide supplemental water for plant use.

Dispersion is the process whereby a chemical, contained in water, deviates from the path that would be expected due to bulk flow. In the process the chemical is mixed with surrounding liquids, causing its concentration to be reduced.

Distillation is a two-stage water treatment method: 1) the liquid is boiled, producing water vapor and leaving most contaminants behind; 2) the water vapor is then condensed back to a liquid. Distillation can be used to remove inorganic chemicals, some non-volatile organic chemicals, and bacteria. Note that volatile chemicals would tend to follow the water vapor.

Drawdown is a lowering of the groundwater surface caused by the withdrawal or pumping of water from a well. It is the difference between the static water level (level of the water in the well when the well is not being pumped) and the pumping (dynamic) water level in a well pumped at a constant flow rate.

Drainage is the process of transporting surface water over a land area to a river, lake, or ocean (surface drainage), or removal of water from a soil using buried pipelines that are regularly spaced and perforated (subsurface drainage).

Drive Shoe - Driveshoes should be found at the base of a metal well casing i.e., steel, when the casing has been driven in the ground. Driveshoes are used to help set a metal well casing into firm competent bedrock and to help advance the well casing and inhibit the casing from splitting. The driveshoes are normally harder and more corrosion resistant than the well casing and they may have a beveled or cutting edge. The driveshoes are hardened by heat treating the metal.


Effluent is the discharge of a contaminant or contaminants with water from animal production or industrial facilities or a waste-water treatment plant (treated sewage effluent), usually into a stream, river, pond (retention basin), or lake.

Erosion is the process or series of processes that removes soils, rock, crop residues, and organic matter from the land surface, transporting it somewhere else where it is then deposited; erosion and deposition are coupled. Erosion is caused by running water, wind, or glaciers. Water droplets begin the soil erosion process by detaching soil particles. Runoff waters transport the detached particles to local and regional streams or lakes. Soil erosion represents the single largest source of nonpoint pollution in the United States.

Eutrophic - One of the trophic status that scientists use to classify lakes. Eutrophic lakes are rich in nutrients and minerals, typically associated with excessive algal growth, and it is common to have low oxygen conditions in the hypolimnion. (see also Lake Trophic State, Oligotrophic, Mesotrophic, and Hypereutrophic)

Eutrophication is the process of surface water nutrient enrichment (usually phosphate and nitrate – fertilizer) causing a water body to fill with aquatic plants and algae. The increase in plant life reduces the oxygen content of the water. Eutrophic lakes often are undesirable for recreation and may not support normal fish populations. Trout, for example, need a relatively high dissolved oxygen (DO) content in the water to thrive and reproduce; carp can tolerate lower DO levels.

Evapotranspiration (ET) is the process of changing soil water into water vapor through the combination of soil evaporation and plant water use, or transpiration. Plant leaves have openings (stomata) under the leaf to allow CO2 to enter the leaf for photosynthesis but letting CO2 in also allows water in the leaf to get out – that escaping water is transpiration.


Field capacity is the amount of water a soil contains after rapid drainage has ceased. It is the water content left in the soil following a period of gravity drainage without the addition of more water.

Fecal coliform  (FC) is a portion of the coliform (rod-shaped) bacteria group originating in the intestinal tract of warm-blooded animals that pass into the environment as feces. Amazingly, from a quarter to more than a half of feces is bacteria.  Fecal coliform is often used as an indicator of the bacteriological safety of a domestic water supply.

The fecal coliform bacterial densities are determined using the membrane filtration technique. The MF procedure uses an enriched lactose medium and an incubation temperature of 44.5 + 0.2 °C. Fecal coliform colonies produced by the M-FC medium are blue, while non-coliform colonies are pale yellow, gray, or a cream color. Since fecal coliform is found in mammalian waste, it is recommended that fecal coliform be absent from potable (drinking) water.

Fecal Streptococcus (FS): The fecal streptococcus group consists of a number of species of the genus Streptococcus, such as: S. faecalis, S. faecium, S. avium, S. bovis, S. equinus, and S. gallinarum. Due to the variation in survival rates, the ratio of FC/FS should not be used as a means of differentiating human and animal sources of bacterial contamination. Fecal streptococcus colonies produced by the KF-Streptococcus broth (a growth medium) are red. For potable water, the fecal streptococcus should be absent.


Gaining stream (effluent stream) is a stream or portion of a stream where flow increases because of discharge from groundwater; groundwater flows from (effluent) the ground into a stream or river. The opposite situation, a losing stream, would be where water flows from a stream or river into (influent) the ground. Note that whether the flow is influent or effluent is from the viewpoint of the ground, not the stream even though the label is put on the stream.

Grains per gallon is an old unit of measurement often used to describe water hardness. One grain per gallon is approximately equal to 17 ppm of various cations. A grain, originally based on the mass of a seed (grain) of some cereal crop, is equal to 64.79891 milligrams.

Groundwater (sometimes written as two words) is water that occupies voids, cracks, or other spaces between particles of clay, silt, sand, gravel or rock within the saturated formation.

Groundwater mining is the removal of groundwater from an aquifer in excess of the rate of natural or artificial recharge. Continued groundwater mining reduces the groundwater supply until it is no longer an economical source of water; the groundwater table keeps dropping deeper.

Groundwater recharge is the process whereby water enters the soil (infiltration), flows downward through the unsaturated rock (percolation), and eventually reaches the saturated zone. Recharge varies from place to place due to the amount of rainfall, surface vegetation and slope, and infiltration/percolation.

Grout is the ring of cement outside of and around the casing of a well. Its purpose is to prevent surface water contamination from flowing down the outside of the well casing and entering the well at the bottom of the casing. After a well has been drilled and a casing is in place, hydraulic cement is injected into the well and forced out of the well, under great pressure, at the bottom of the casing where it spreads up along the outside of the casing to the surface. It is left to harden for several days and then any cement left in the inside of the casing is removed by the drilling rig which, after all, is designed to drill through rock so a little cement won’t stop it. The drilling rig can then continue to drill deeper in a search for enough groundwater to meet the needs of the well owner. All modern wells should be grouted.

Grouting - For our specific field, i.e. well drilling and construction, grouting is the process of filling the annular space (the space between the final well casing and the borehole wall), with a material called grout (usually some type of cement) to decrease the permeability of this artificially-created conduit.  If done properly, this would prevent any surface contamination from traveling down the outside of the well casing to the bottom of the casing, into the aquifer, and into the well at the bottom of the casing. 

In domestic well drilling well construction or abandonment, grouting is best performed using a tremie pipe to fill the annular space using a grout pump and grout from the bottom up. The grout is poured into the borehole and the tremie pump forces the grout to flow down and out of the casing at its bottom and up the outside of the casing all the way up to the surface. After the grout hardens, the drilling rig simply drills through any grout left inside the casing and continues to deepen the hole.


Hardness: The hardness of a water is a measure of the concentration of the multivalent cations (positively charged ions with more than one positive charge) in the water, but primarily it is equivalent to the calcium and magnesium concentration of the water (iron and manganese can sometimes be significant contributors). Hardness is typically reported as mg /L as CaCO3 (calcium carbonate), but it may also be reported as grains per gallon (1 gpg (US) = 17.12 mg CaCO3/L ). The contributions of other cations to hardness are added to the calcium hardness by calculating how much additional calcium would be needed to match the hardness produced by the other cations (calcium equivalents) to produce (total) hardness as CaCO3/L equivalents. Hardness Classification: Soft: 0 to 17 mg CaCO3/L; Slightly Hard: 17 to 60 mg/L; Moderately Hard 60 to 120 mg/L; Hard 120 to 180 mg/L; and Very Hard > 180 mg/L. The best water is probably slightly to moderately hard; drinking nothing but distilled water (no hardness at all) is a bad idea.

Health Advisories (HA): New research may suggest that an unregulated parameter could have a significant impact on human health but that link has not yet been definitively established. While research continues on that parameter, the EPA may issue a health advisory as a potential warning to the drinking water community. A health advisory is not yet a regulatory standard and, depending on the result of further research, may or may not become a standard. See EPA Health Advisory PDF to learn more.

Health Advisory Level (HAL) is a non-regulatory health-based chemical concentration in drinking water that results in no adverse health risks when a given amount of water is ingested over exposure periods ranging from one day to a lifetime.

Heterotrophic Bacteria: Heterotrophic plate count is a procedure for estimating the number of live heterotrophic (cannot produce its own food) bacteria in the water. Colonies may form from bacteria pairs, clusters, or from single cells, which can be termed as "colony-forming units". The colonies are relatively small/compact and do not encroach on each other. This procedure will not work for high concentrations of bacteria although the original water sample can be diluted to reduce the concentration of bacteria to a level that will not overwhelm a plate count. Such a test is typically performed on high purity water, for pilot treatment-facility-performance evaluations, and on pilot-scale testing.

Hydraulic conductivity is a term, similar but not identical to permeability (q.v.), which is used to describe the ease with which water moves through soil or a saturated geologic material. Hydraulic conductivity is influenced by the type of material comprising the aquifer (sand, gravel, rock, limestone, sandstone, clay), the slope of the water table, the type of fluid, and the degree to which existing pores are interconnected.

Hydraulic gradient is the slope of the water surface in an aquifer. The hydraulic gradient indicates the direction groundwater will flow. Water always flows from higher water table elevations to lower water table elevations. All other factors being equal, flow is greater when the hydraulic gradient is steeper.

Hydrologic cycle describes the constant movement of water above, on, and below the earth's surface. Processes such as precipitation, evaporation, transpiration, condensation, infiltration, advection, and runoff comprise the cycle. Within the cycle, water changes forms (solid, liquid, vapor) in response to the Earth's climatic conditions.

Hypereutrophic - Is a one of the trophic states for a lake that is associated with very nutrient-rich water with low transparency or visibility, high chlorophyll content, and many algal blooms. In some cases, these lakes are phosphate or nitrogen limiting. (see also Lake Trophic State, Oligotrophic, Mesotrophic, and Eutrophic)

Hypolimnion - The denser bottom layer of a thermally stratified lake, meaning colder water at the bottom and warmer at top with very little mixing between the layers.


Infauna - The aggregate of animals that burrow into and live in the bottom deposits of an ocean, river, or lake; these animals include clams, snails, polychaetes, flatworms, and small crustaceans. Infauna are vital to a healthy ecosystem.

Infiltration is the downward entry of water into the soil. The infiltration rate is a function of surface wetness, soil texture, surface residue cover, irrigation application or precipitation rate, surface topography, and other factors.

Iron (Fe): The MCL is 0.3 mg/L. Iron is regulated under a secondary drinking water standard because of the aesthetic problems associated with elevated iron.


Lake Trophic State - A system used by scientists to classify lakes. (see also Oligotrophic, Mesotrophic, Eutrophic, and Hyper Eutrophic)

Leaching is the removal of chemicals from rock and soil by dissolving them into water which then carries them away.

Lead (Pb): The MCL is 0.005 mg/L. Symptoms of lead poisoning start as: abdominal pains, constipation, fatigue, depressed appetite and decreased endurance, but long-term exposure may lead to nerve and kidney damage and anemia. For City water, the lead limit is 0.015 mg/L. (Note: There is no safe level of lead, MCLG - Zero).

Losing stream (influent stream) is a stream or portion of a stream that discharges water into the groundwater. See Gaining stream.

Low permeability layers include soil, sediment, or other geologic material that inhibit water movement. These layers may serve as a base material or confining beds for an aquifer. This may be caused by a fragipan (a layer of soil that is much less permeable than the layers above and below) or a silt clay horizon in the soil. In general, clayey soils and shales usually have low permeabilities.


Magnesium (Mg): No specific recommendation, but high magnesium is associated with higher hardness and total dissolved solids which can lead to aesthetic problems.

Manganese (Mn): The MCL is 0.05 mg/L. Manganese is regulated under a secondary drinking water standard because of the aesthetic problems associated with elevated levels of manganese. Elevated manganese levels can disrupt the nervous system and regeneration of hemoglobin. For freshwater, the concentration should be less than 1.5 mg/L.

Maximum contaminant levels (MCLs) are legally enforceable drinking water standards required by the U.S. Safe Drinking Water Act. Standards set by the Environmental Protection Agency establish the maximum permissible concentration of selected contaminants in public water supplies. Contaminants are included on the list if they pose a public health risk. For example, 10 ppm is the MCL for nitrate-nitrogen (NO³- N).

Maximum contaminant level goals (MCLGs) are public drinking water standards that serve as nonenforceable goals for selected contaminants contained in drinking water that pose no health risk to people over a lifetime of exposure. A MCLG is a suggested level set by the EPA as a guideline for water utilities.

Mercury (Hg): The MCL is 0.002 mg/L for organic mercury such as methyl mercury. Organic forms of mercury are much more easily assimilated by the human body than elemental mercury. Mercury has been associated with kidney disease. For freshwater, the concentration should be less than 0.00005 mg/L.

Mesotrophic - Have moderate levels of nutrients, slightly more diversity of fish species and higher levels of algae and slightly lower secchi disc depth. Unlike oligotrophic lakes, mesotrophic lakes can stratify in the summer. Mesotrophic lakes have a seasonal thermocline and a hypolimnion. (see also Lake Trophic State, Oligotrophic, Eutrophic, and Hypereutrophic)

Methemoglobinemia or blue baby syndrome is the condition that limits the oxygen-carrying capacity of red blood cells. The condition occurs when bacteria in the digestive tract convert nitrate to nitrite. Nitrite reacts with hemoglobin in the blood, producing methemoglobin which cannot carry oxygen. The resulting oxygen starvation causes a bluish discoloration of the body. The condition is largely confined to infants less than 9 months old. Excessive amounts of nitrates may be ingested with water or food. Often foods, such as fresh vegetables, are a major source of nitrates.


Nickel (Ni): MCL has not been established, but for freshwater, the concentration should be less than 0.1 mg/L. The element is detected using flame atomic absorption. There is no specific standard for nickel. Nickel may cause dermatitis and nasal irritation.

Non-point source (NPS) pollution is a source of surface or groundwater pollution originating from diffuse areas without well-defined (point) sources. The most common examples of NPS are chemicals (such as pesticides and fertilizer) that enter surface water during runoff events from cropland and turfgrass, and soil erosion from cultivated cropland and construction sites.


Oligotrophic - One of the trophic status that scientists use to classify lakes. Oligotrophic lakes have very low nutrients, low productivity and limited diversity of fish. These lakes tend to be cold with high levels of oxygen, low levels of algae, high secchi disc depth. (see also Lake Trophic State, Mesotrophic, Eutrophic, and Hypereutrophic)


Part-per-million (ppm) is a measure of the concentration of a dissolved material in terms of a mass ratio (milligrams per kilogram, mg/kg). 1 ppm means that one part of a contaminant is present for each million parts of water. For water analysis, parts per million often is presented as a mass per unit volume (milligrams per liter, mg/L). There are one million milligrams of water in one liter.

Perched water tables occur when a low permeability material, located above the water table, blocks or intercepts the downward flow of water from the land surface. Water mounds up above the impermeable material, creating another saturated zone with a water table (Episaturation) perched above the main water table below.

Permeability is the property of porous materials indicating the ease with which liquids or gases will be transmitted through a soil or other porous material. Permeabilities are not affected by changing the type of liquid. It is similar but not identical to hydraulic conductivity (q.v.).

Periphyton - A complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. It serves as an important food source for invertebrates, tadpoles, and some fish. It can also absorb contaminants, removing them from the water column and limiting their movement through the environment. (Source)

pH is a numerical measure of the acidity or alkalinity of water. The pH scale ranges from 0 (very acidic) to 14 (very alkaline). A pH of 7 is neutral.The technical definition of pH is that it is a measure of the activity of the hydrogen ion (H+) and is reported as the reciprocal of the logarithm of the hydrogen ion activity. Therefore, water with a pH of 7 has 10-7 moles per liter of hydrogen ions (H+) whereas water with a pH of 6 has 10-6 moles per liter of H+.

Phosphate (PO₄⁻³): There is no MCL for phosphate. In surface waters, phosphate is typically a limiting plant nutrient. The recommended maximum concentration in rivers and streams is a concentration of 0.1 mg/L of total phosphate. Too much phosphate in surface water can lead to eutrophication (q.v.).

Point-of-entry (POE) treatment is the treatment of all water entering a house, farmstead, or other facility, regardless of its intended use. Anion exchange is an example of POE treatment to remove nitrates.

Point-of-use (POU) treatment is treatment of water at the point it is used. A common example would be water treatment at the kitchen sink for drinking and cooking uses. Reverse osmosis, distillation, and ozonation are examples of POU treatment methods.

Point source (PS) pollution is surface or groundwater pollution that originates from a well-defined source. Examples include: industrial effluent, large animal containment facilities, city waste-water treatment discharges, or chemical spills. Point sources commonly are associated with pipeline discharges of some type.

Pollutant is any unwanted chemical or change in physical property that renders a water supply unfit for its intended use.

Porosity is the ratio of the volume of open spaces or voids to the total volume of a porous material. For example, a sand and gravel deposit may have 20 percent porosity (which is quite high); a sponge would have an even greater porosity. Porosity determines the amount of water that can be stored in a saturated formation. A saturated formation 100 feet thick with a porosity of 20 percent could store an equivalent water depth of approximately 20 feet.

Potable water supply is a source of water that can be used for human consumption.

Precipitation is the process in which water vapor condenses in the atmosphere to form water droplets that fall to the earth as rain, sleet, snow, or hail. As an example, Nebraska's long-term annual precipitation varies from 16 inches in the west to 34 inches in the southeast. Annual deviations can be greater than 30 percent. Any ice or snow collected in a rain gauge is allowed to melt to see how many inches of rain equivalent it would be.

Pumping water level (dynamic level) is the water level in a well when the pump is operating and water is being removed from the well.


Recharge area is the area where water predominantly flows downward through the unsaturated formation (zone) to become groundwater.

Reference dose (RfD) is the maximum daily exposure to a chemical that is judged to be without risk of adverse systemic health effects over a person's lifetime. It formerly was called the Acceptable Daily Intake.

Reverse osmosis (RO) is a water treatment method used to remove dissolved inorganic chemicals and suspended particulate matter from a water supply. Water, under pressure, is forced through a semipermeable membrane that removes molecules larger than the pores of the membrane. Large molecules are flushed into waste waters. Smaller molecules are removed by an activated carbon filter.

Runoff is precipitation or irrigation water that does not infiltrate into the soil but flows over the land surface, eventually making its way to a river, lake, or an ocean.

Running Average Suppose that you had a long record of daily average temperatures for a particular area. There may be a few days when the average temperature is much higher or much lower than most other days. To smooth out short-term spikes and dips and make it easier to see longer-term trends, you could use a running average. In this example, if, for each day, you took the average temperature of that day and average it with the average temperatures of the two days before and after it, you would have a 5-day running average for that day. The five-day running average for the next day would be the average of that day averaged with the averages of the two preceding and two following days, hence, a running average. For a running average, you need to specify over how many time units (hours, day, weeks, months, years) you are going to average (like the 5-day running average).


Saturated formation (zone) is the portion of a soil profile or geologic formation where all voids, spaces or cracks are filled with water. No air is present. There may be multiple water-bearing formations within a saturated formation. These water-bearing formations often are separated by layers of clay or other impermeable layers.

Saturated thickness (zone) is the total thickness of a saturated formation.

Seepage is the movement of water into or through a porous material. Seepage occurs from canals, ditches, and other water storage facilities; the water seeps into the ground. It sometimes is used to describe water escaping from municipal landfill sites (such water is called leachate).

Selenium (Se): The MCL is 0.05 mg/L. Selenium is associated with hair or fingernail loss, numbness of fingers and toes, and circulatory problems. For freshwater the concentration should be less than 1.5 mg/L.

Shock chlorination is the addition of chlorine, intended to disinfect a water supply system, into a well and all water distribution pipelines. Shock chlorination is recommended when coliform bacteria are detected, or after system repairs. Treated (chlorinated) water, with a concentration of at least 200 ppm chlorine, is pumped throughout the distribution system and allowed to remain in the lines for at least 24 hours before flushing the system with untreated water. You should not use the water that has been shock chlorinated.

Silver (Ag): The MCL is 0.10 mg/L. Silver is associated with causing discoloration (gray) of the skin. For freshwater the concentration should be less than 0.0003 mg/L.

Sodium (Na): No MCL has been set. For individuals on low-sodium diets a general recommendation of no more than 20 mg/L is used.

Specific capacity expresses the productivity of a well. Specific capacity is obtained by dividing the well discharge rate by the well drawdown (how far the water level in the well drops from the static level) while pumping. It is expressed in units of gallons per minute (gpm) per foot of drawdown.

Specific yield is the ratio of the volume of water that will drain from a unit volume of aquifer by gravity flow.

Spring is the point of natural groundwater discharge to a soil surface, river, or lake.

Static water level is the water level in a well located in an unconfined aquifer when the pump is not operating. The static water level is the surface of the water-bearing formation and typically is synonymous with the water table.

Strontium (Sr): No MCL has been set, but the element is analyzed using a nitrous oxide-acetylene flame. The primary concern is the presence of a radioactive isotope of strontium, known as Strontium-90.

Sulfate (SO₄⁻²): The drinking water limit is 250 mg/L. Sulfate (SO₄⁻²) is widely distributed in natural waters, but is typically less than a few mg/L. In Northeastern Pennsylvania, the primary sources of sulfate in surface waters and groundwater include: acid mine drainage, acid deposition, and mineral oxidation. It is regulated under a Secondary Standard because of taste and aesthetic problems; sulfates can have laxative effects.

Sulfite (SO₃⁻²): May occur in boilers and boiler feedwater treated with sulfite to control dissolved oxygen levels, natural waters containing industrial waste, and in wastewater treatment plant effluents using sulfur dioxide to dechlorinate the effluent.


Thallium (TI): The MCL is 0.002 mg/L, but a MCL Goal is 0.0005. Thallium is associated with hair loss, changes in the blood, and kidney, digestive, and liver problems.

Thermocline -This is a condition that forms in a lake and other water bodies. A thermocline is the transition layer between the warmer mixed water at the surface and the cooler deep water below and this layer is associated with a rapid change typically in both temperature and oxygen content.

Tin (Sn): No MCL has been established for tin. Metallic tin is not toxic but methylated tin is

Total Kjeldahl Nitrogen (TKN): There is no MCl for total Kjeldahl nitrogen. This parameter is used to measure the total amount of organic nitrogen in water and is typically used for surface water and groundwater investigations associated with domestic or agricultural contamination.

Transmissivity is the capacity of an aquifer to transmit water. It is dependent on the water-transmitting characteristics of the saturated formation (hydraulic conductivity) and the saturated thickness. For example, sand and gravel formations typically have greater hydraulic conductivities than sandstone formations. The sand and gravel will have a greater transmissivity if both formations are the same thickness.

Total Dissolved Solids (TDS) is a water quality parameter defining the concentration of dissolved organic and inorganic chemicals in water. Total Dissolved Solids is determined by filtering a measured volume of sample through a standard glass fiber filter. The filtrate (i.e., filtered liquid) is then evaporated to dryness at a constant temperature of 180 °C. After suspended solids are filtered from water and water is evaporated, dissolved solids remain in solution . High total dissolved solids may affect the aesthetic quality of the water (the water looks dirty), interfere with washing clothes, and corroding plumbing fixtures. For aesthetic reasons, there is a secondary standard  of 500 mg dissolved solids/L for potable water supplies.

Total Dissolved Solids concentrations depend on the geologic material water passes through in the saturated and unsaturated aquifer zones , and on the quality of the infiltrating water. 

Total Dissolved Solids commonly include calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride and silica. Total Dissolved Solids range from less that 100 ppm in small tributary streams to greater than 1,000 ppm for larger rivers.

Turbidity: Turbidity is a measure of the cloudiness or opaqueness of the water and is measured in nephelometric turbidity units (ntu). The turbidity is influenced by the amount and nature of suspended (not dissolved) organic and inorganic material in water. Typically, the higher the concentration of the suspended material the greater the turbidity. A value of 1 ntu is recommended for drinking water, since higher turbidities could cause aesthetic problems or inhibit the ability of a system to disinfect the water. The source of turbidity could be fine sand, silt, and clay (i.e., soil separates), organic material, particles of iron and manganese or other metal oxides, rust from corroding piping, or carbonate precipitates. Turbidity measurements are typically not made on surface water sources - see Total suspended solids.

Total Solids: The total amount of solids in the sample, which includes: dissolved, suspended, and volatile.

Total Suspended Solids: A fixed volume of sample is filtered through a preweighed and washed glass fiber filter. The filter is then rinsed and dried at 103 to 105 °C. The change in the weight of the filter represents the weight of the material that was suspended in the water. This test is typically done for surface water supplies and wastewater treatment plants. For drinking water, turbidity is a parameter that is typically monitored.

Total Dissolved Solids: Is determined by filtering a measured volume of sample through a standard glass fiber filter. The filtrate (i.e., filtered liquid) is then evaporated to dryness at a constant temperature of 180 C. High total dissolved solids may affect the aesthetic quality of the water, interfere with washing clothes and corroding plumbing fixtures. For aesthetic reasons, a limit of 500 mg dissolved solids/L is typically recommended for potable water supplies.

Total Volatile Solids: The residue left after allowing the water to evaporate is heated to a temperature of 500 °C, driving off any volatile matter. The change in the weight of the residue represents the amount of suspended or dissolved solids that are volatile organics. This parameter is typically used in wastewater treatment plants because it provides an estimate of the organic matter content within the waste stream.


Unsaturated formation (vadose zone) is a layer within the soil or other geologic material, usually located between the land surface and a saturated formation, where the voids, spaces, or cracks are filled with a combination of air and water.


Vanadium (V): Currently there is no specific MCL for vanadium. Vanadium may cause respiratory problems and inhibit Na and K in ATP production.


Watersheds are regional basins drained by or contributing water to a particular point, stream, river, lake, or ocean. Watersheds range in size from a few acres to large areas of the country.

Water table is the surface of the saturated zone in an unconfined aquifer.


Yeast and Molds: Yeasts and molds are fungi. A fungus is a colorless (i.e., lacking chlorophyll) plant with practically no differentiation of cell structure. Yeasts are small, single-celled forms that reproduce by budding or spore formation. Molds produce spores for both asexual and sexual reproduction. Yeast and mold analysis is typically done on air-borne samples and surface wipes.


Zinc (Zn): The MCL is 5 mg/L, because of problems with the aesthetic quality due to the metallic taste of zinc.

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