Knowledge Base

PALATABLE WATER — Water, at a desirable temperature, that is free from objectionable tastes, odors, colors, and turbidity.

PAN — (1) A basin or depression in the earth, often containing mud or water. (2) A natural or artificial basin used to obtain salt by evaporating brine.

PARAPET WALL — A solid wall built along the top of a dam for ornament, for the safety of vehicles and pedestrians, or to prevent overtopping.

PARTICULATE LOADING — The mass of Particulates per unit volume of water.

PARTICULATE MATTER — (Water Quality) In water pollution, particulate matter describes solid material in either the solid or dissolved states. Insoluble particulate matter includes particulate substances that either settle from water that is allowed to stand or are removed by passing the water through a filter. Sand, clay, and some organic matter constitute insoluble particulate matter. Dissolved substances that will neither settle if water is allowed to stand nor be removed by passage through a filter, but which will be recovered if the water is allowed to evaporate, are called dissolved particulate matter. Salt is an example of this type of particulate matter. In air pollution, particulate matter is used to describe either solid particles or liquid droplets that are carried by a stream of air or other gases.

PARTICULATES — Very small solids suspended in water. They can vary in size, shape, density, and electrical charge and can be gathered together by Coagulation and Flocculation.

PEAK FLOW — The maximum instantaneous discharge of a stream or river at a given location. It usually occurs at or near the time of maximum stage.

PEAKING — Typically describes the peak water demand for a municipal water system and is expressed as a ratio of the base demand level, e.g., 2:1 peaking represents a peak demand that is twice the base demand.

PEAK LOAD (POWER) — The maximum load in a stated period of time. Usually it is the maximum integrated load over an interval of one hour which occurs during the year, month, week, or day. It is used interchangeably with Peak Demand.

PEAK USE RATE — The maximum periodic rate of consumptive use (Evapotranspiration) of water by plants.

PER-CAPITA WATER USE — The water produced by or introduced into the system of a water supplier divided by the total residential population; normally expressed in gallons per-capita per day (gpcd).

PERCENT SATURATION — The amount of a substance that is dissolved in a solution compared to the amount that could be dissolved in it.

PERCHED GROUND WATER — Ground water in a saturated zone of material underlain by a relatively impervious stratum which acts as a barrier to downward flow and which is separated from the main ground water body by a zone of unsaturated material above the main ground water body.

PERCHED STREAMS — Perched streams are either Losing Streams or Insulated Streams that are separated from the underlying ground water by a zone of aeration.

PERCHED WATER TABLE — The top of a Zone of Saturation that bottoms on an impermeable horizon above the level of the general water table in the area. Is generally near the surface, and frequently supplies a hillside spring.

PERCOLATING WATERS — Underground waters whose course and boundaries are incapable of determination. Waters which pass through the ground beneath the earth's surface without a definite channel. It is presumed that ground waters percolate.

PERCOLATION — (1) The movement, under hydrostatic pressure, of water through the interstices of a rock or soil. Also, the movement of water within a porous medium such as soil without a definite channel. (2) The entrance of a portion of the streamflow into the channel materials to contribute to ground water replenishment. (3) Slow seepage of water through a filter.

PERCOLATION, DEEP — The amount of water that passes below the root zone of the crop or vegetation.

PERCOLATION PATH — The course followed by water moving or percolating through any permeable material or under a dam which rests on a permeable foundation.

PERCOLATION POND — Refers to a pond (usually man-made) designed to allow treated wastewater effluent to percolate slowly into the ground. The pond acts as a holding facility while gravity allows the water to percolate or seep through the soil or other unconsolidated medium into the local water table (usually the surfacial aquifer).

PERCOLATION RATE — The rate, usually expressed as a velocity, at which water moves through saturated granular material. Also applies to quantity per unit of time of such movement and has been used erroneously to designate Infiltration Rate or Infiltration Capacity.

PERCOLATION TEST — A soil test to determine if soil will take sufficient water seepage for use of a septic tank.

PERENNIAL CROPS — Those plants that live and evapotranspire throughout the year (365 days).

PERENNIAL STREAM — A stream that flows from source to mouth throughout the year.

PERENNIAL YIELD (GROUND WATER) — The amount of usable water of a ground water reservoir that can be withdrawn and consumed economically each year for an indefinite period of time. It cannot exceed the sum of the Natural Recharge, the Artificial (or Induced) Recharge, and the Incidental Recharge without causing depletion of the groundwater reservoir.

PERFECTED WATER RIGHT — A water right which indicates that the uses anticipated by an applicant, and made under permit, were made for Beneficial Use. Usually it is irrevocable unless voluntarily canceled or forfeited due to several consecutive years of nonuse.

PERFECTED WATER PERMIT — A permit issued after the permittee has initiated Beneficial Use of water in accordance with the terms and conditions of the conditional water permit. The perfected water permit is the instrument of conveyance of a water right.

PERFECTION — The process of meeting terms and conditions of a water right permitting process which results in a Perfected Water Right.

PERFORATION OF WELLS — Holes in the casing of wells which allow water to flow into the well.

PERMANENT CONTROL — A stream-gaging control which is substantially unchanging and is not appreciably affected by scour, fill, or backwater.

PERMANENT HARDNESS — Water hardness that cannot be reduced or removed by heating the water, a reflection of the presence of dissolved calcium, magnesium, iron and other divalent metal ions. These ions will react to form insoluble precipitates.

PERMANENT MONUMENT — Fixed monuments or reference markers placed away from the dam which allow movements in the horizontal and vertical Control Points on the dam to be observed by using accurate survey procedures.

PERMISSIBLE VELOCITY — (Hydraulics) The highest velocity at which water may be carried safely in a channel or other conduit. Also, the highest velocity that can exist through a substantial length of conduit and not cause scouring of the channel.

PERMIT — (1) (Water Right) A written document which grants authority to take unused water and put it to Beneficial Use. (2) (Discharge) A legally binding document issued by a state or federal permit agency to the owner or manager of a point source discharge. The permit document contains a schedule of compliance requiring the permit holder to achieve a specified standard or limitation (by constructing treatment facilities or modifying plant processes) by a specified date. Permit documents typically specify monitoring and reporting requirements to be conducted by the applicant as well as the maximum time period over which the permit is valid.

PERMITTED WELL — A well from which water is used for other than a domestic use and which has received a permit for a Beneficial Use from the water regulatory body or other appropriate official.

PERSPIRATION — The fluid, consisting of water with small amounts of urea and salts, that is excreted through the pores of the skin by the sweat glands; sweat.

PERSPIRE — To produce sweat or salty water from glands in the skin. A natural way of cooling the body by the evaporation of water.

PERVIOUS — Allowing passage through, as a material to water.

PERVIOUS PAVING — Paving material that allows water to penetrate to the soil below.

PERVIOUS ZONE — A part of the cross section of an Embankment Dam comprising material of high permeability.

PESTICIDE — Any chemical agent used for the control of specific organisms, for example, Insecticides, Herbicides, Fungicides, etc.

PHREATIC — Of or relating to ground water.

PHREATIC LINE — The line marking the upper surface of the Zone of Saturation in the soil.

PHREATIC SURFACE — A term equivalent to the Groundwater Surface or the Water Table; the free surface of ground water at atmospheric pressure.

PHREATIC WATER — Synonymous with the Zone of Saturation.

PIEZOMETER — (1) An instrument used to measure pressure head in a conduit, tank, soil, etc. It usually consists of a small pipe or tube tapped into the side of the container, so that the inside end is flush with, and normal to, the water face of the container and is connected with a manometer pressure gage, mercury or water column, or other device for indicating pressure head. (2) An instrument for measuring pore water pressure within soil, rock, or concrete. (3) Also, an instrument for measuring the compressibility of liquids.

PIEZOMETER (OPEN WELL) — A well structure or tube which allows the level of saturation within a dam to be measured.

PIEZOMETRIC HEAD — Synonymous with Hydraulic Head, which is now commonly used.

PIEZOMETRIC SURFACE — An imaginary surface that everywhere coincides with the static level of the water in the aquifer. This term is now generally considered to be obsolete, being replaced by the term Potentiometric Surface.

PIPELINE — A conduit of pipe, especially one used for the conveyance of water, gas, or petroleum products.

PIPING — The progressive development of erosion of a dam structure by seepage, appearing downstream of the dam as a hole or seam discharging water that contains soil particles.

PIRATE STREAM — One of two streams in adjacent valleys that has been able to deepen its valley more rapidly than the other, has extended its valley headward until it has breached the divide between them, and has captured the upper portion of the neighboring stream.

PITOT TUBE — An instrument used to measure the velocity of flowing water, with the velocity head of the stream an index of velocity. It consists essentially of an orifice held to a point upstream in the water, connected with a tube in which the rise of water due to velocity head may be observed and measured. It also may be constructed with an upstream and downstream orifice, with two water columns, in which case the difference in height of the water columns in the tubes is the index of velocity.

PITTING — The construction of pits or basins of suitable capacity and distribution to retain water and increase infiltration on rangeland.

PLACE OF USE — The specific location, typically documented in a water right permit, where water is applied or used. A water user cannot use water at another location without transferring the right or obtaining a new right.

PLAN — A compilation of goals and objectives, policy statements, and implementation strategies for guiding the physical, social, and/or economic development of an area or region; may be comprehensive or may relate to a specific resource, i.e., a Water Resource Plan which assesses both sources and use of water and develops strategies for their most effective and efficient use.

PLUME — (1) (Ecology) A space in air, water, or soil containing pollutants released from a point source. (2) (Water Pollution) A relatively concentrated mass of emitted chemical contaminants spreading in the environment. In surface water, the effluent added to a receiving stream near a point source. For example, when a heated-water discharge is added to a stream, the heated water does not mix immediately with the stream water. The mass of hot water remains detectable for some distance downstream. In groundwater, the Leachate leaking down-gradient from a site of buried waste material.

PLUNGE — To thrust or cast oneself into, or as if into, water.

PLUVIAL — (1) Of having to do with rain; rainy. (2) To flow, pour, or fill. (3) (Geology) Formed or caused by the action of rain, as a pluvial deposit. (4) (Geology) More specifically, the two or more Wisconsin stages, of the late Pleistocene age (epoch), when the western United States waterbasins were filled with lakes. The Early Pluvial period consisted of periods of high humidity so remote as to have left no clear-cut shore features; the Postpluvial period represented a period of desiccation following the last high lake stage.

PLUVIAL LAKE — A lake formed during a pluvial (rainy) period.

PLUVIAL PERIOD — A period of increased rainfall and decreased evaporation, which prevailed in nonglaciated areas during the time of ice advance elsewhere.


POLDER — An area of low-lying land, especially in the Netherlands, that has been reclaimed from a body of water and is protected by dikes.

POLICY — (Water Planning) A statement of governmental intent against which individual actions and decisions are evaluated. The wording of policies conveys the level of commitment to action, for example, policies which use the word "shall" are mandatory directives, while those using the word "should" are statements of direction to be followed unless there are compelling reasons to do otherwise.

POLISHING — (Water Quality) The removal of low concentrations of dissolved, recalcitrant organic compounds from either water intended for human consumption or wastewater that has been subjected to Primary and Secondary Wastewater Treatment. The passage of water through a charcoal filtering device is a frequently employed polishing technique.

POLLUTANT — (1) Something that pollutes, especially a waste material that contaminates air, soil, or water. (2) Any solute or cause of change in physical properties that renders water unfit for a given use.

POLLUTED — Something which contains foreign substances.

POLLUTION — Any alteration in the character or quality of the environment which renders it unfit or less suited for certain uses. With respect to water, the alteration of the physical, chemical, or biological properties by the introduction of any substance that adversely affects any beneficial use. Under the Clean Water Act (CWA), for example, the term is defined as the manmade or man-induced alteration of the physical, biological, chemical, and radiological integrity of water.

POLLUTION INDICATOR ORGANISM — (Water Quality) A plant or animal species that is not normally present in an aquatic environment unless the body of water has been subjected to damage by pollution. For example, Escherichia coli is a bacterium that is not found in the aquatic environment unless the system has been contaminated by the addition of fecal material. The organism signals the presence of pollution.

POND — A body of water smaller than a lake, often artificially formed.

POND, WASTEWATER STABILIZATION — (Water Quality) An impoundment area for water, natural or artificial, into which untreated or partially treated wastewater is discharged and in which natural purification and stabilization processes take place under the influence of sunlight, air, and biological activity.

PONDAGE — (1) The holding back of water for later release for power development above the dam of a hydroelectric plant to: (a) equalize daily or weekly fluctuations of streamflow, or (b) to permit irregular hourly use of water by the wheels to take care of fluctuations in the load demand. (2) The water so held back and later released. (3) The storage capacity available for the use of such water.

POOL — A deep reach of a stream. The reach of a stream between two riffles; a small and relatively deep body of quiet water in a stream or river. Natural streams often consist of a succession of pools and riffles.

POPULATION — (Statistics) The total number of potential observations in a specific category, for example, the human population of a particular city, or the number of animals of a particular species within a defined area. Typically, measurements of the behavior and characteristics of the population are not possible and therefore a Sample is selected which, if an Unbiased Sample, will, even in its limited numbers, be representative of the characteristics of the total population.

POPULATION DENSITY — (1) The number per unit area of individuals of any given species at a given time. (2) (Water Planning) The number of people in a given area. The number may be obtained by multiplying the number of dwelling units per unit area (e.g., square mile, square kilometer, acre, etc.) by the number of residents per dwelling unit.

POROSITY — Most generally, porosity is the property of containing openings or interstices. In rock or soil, it is the ratio (usually expressed as a percentage) of the volume of openings in the material to the bulk volume of the material. With respect to water, porosity is a measure of the water-bearing capacity of a formation. However, with respect to water extraction and movement, it is not just the total magnitude of porosity that is important, but the size of the voids and the extent to which they are interconnected, as the pores in a formation may be open, or interconnected, or closed and isolated. For example, clay may have a very high porosity with respect to potential water content, but it constitutes a poor medium as an aquifer. More important in this respect are a formation's Effective Porosity (defined below) and its Specific Retention.

POROSITY, EFFECTIVE — The amount of interconnected pore space in a material available for fluid transmission; expressed as a percentage of the total volume occupied by the interconnecting interstices. Porosity may be primary, formed during deposition or cementation of the material, or secondary, formed after deposition or cementation, such as fractures.

POROUS — A condition which allows liquids to pass through.

POTENTIAL — (1) (Hydrology and Hydraulics) Any of several scalar variables, each involving energy as a function of position or condition; of relevance here is the fluid potential of ground water. (2) (Water Quality) A water quality issue or problem identified by a river authority as being a potential problem, or a problem without current supporting data.

POTENTIAL DROP — Difference in total head between two Equipotential Lines.

POTENTIAL ENERGY — The energy available in a substance because of position (e.g., water held behind a dam) or chemical composition (hydrocarbons). This form of energy can be converted to other, more useful forms (for example, hydroelectric energy from falling water).

POTENTIAL EVAPOTRANSPIRATION — (1) The maximum quantity of water capable of being evaporated from the soil and transpired from the vegetation of a specified region in a given time interval under existing climatic conditions, expressed as depth of water. (2) The water loss that will occur if at not time there is a deficiency of water in the soil for use by vegetation.

POTENTIAL NATURAL WATER LOSS — The water loss during years when the annual precipitation greatly exceeds the average water loss. It represents the approximate upper limit of water loss from the type and density of vegetation native to a basin, under conditions of actual moisture supply and other basin characteristics, in contrast to Potential Evapotranspiration which represents a hypothetical condition where there is no deficiency of water in the soil for use by the type and density of vegetation that would develop.

POTENTIAL RATE OF EVAPORATION — The rate of evaporation under the existing atmospheric conditions from a surface of water that is chemically pure and has the temperature of the atmosphere.

POTENTIAL SUPPLY — That part of the resource base that has the potential for development or further expansion.

POTENTIAL YIELD (or WELL CAPACITY) — The maximum rate at which a well will yield water under a stipulated set of conditions, such as a given drawdown, pump, and motor or engine size. Well capacity may be expressed in terms of gallons per minute, cubic feet per second, or other similar units.

POTENTIOMETRIC SURFACE — A surface which represents the static head of ground water in tightly cased wells that tap a water-bearing rock unit (i.e., aquifer). In relation to an aquifer, the potentiometric surface is defined by the levels to which water will rise in tightly cased wells. If the head varies significantly with depth in the aquifer, then there may be more than one potentiometric surface. The Water Table is a particular potentiometric surface for an Unconfined Aquifer.

PRECIPITABLE WATER — The total water vapor contained in an atmospheric column of unit cross-sectional area; expressed in terms of water of the same cross-sectional area.

PRECIPITANT — An agent added to a liquid mixture to encourage the formation of solid materials that will settle from the mixture. For example, alum (aluminum sulfate) is added to sewage to promote the formation of Floc, which facilitates the removal of organic materials from the wastewater.

PRECIPITATE — A solid which forms from a liquid suspension as a result of a chemical reaction. The material (floc) is insoluble in water and will settle out over time.

PRECIPITATION — As used in Hydrology, precipitation is the discharge of water, in liquid or solid state, from the atmosphere, generally onto a land or water surface. It is the common process by which atmospheric water becomes surface or subsurface water. The term "precipitation" is also commonly used to designate the quantity of water that is precipitated. Forms of precipitation include drizzle, rainfall, glaze, sleet, snow, graupel, small hail, and hail. Also, the process of separating mineral constituents from a solution by evaporation (halite, anhydrite) or from magma to form igneous rocks.

PRECIPITATION, EFFECTIVE — In agriculture, that portion of the rainfall that remains in the soil and contributes to crop growth.

PRECIPITATION GAGE — A device used to collect and measure precipitation.

PRECIPITATION, INITIAL — Precipitation at the beginning of a storm before the depression storage is fully filled up.

PRECIPITATION, INTENSITY — The amount of precipitation collected in a unit time interval.

PRECIPITATION, PROBABLE MAXIMUM — The amount of precipitation that is the physical upper limit for a given duration over a particular basin.

PREFERRED USE — A use given some sort of preference not given other uses. Preference can take many forms, depending on state law. One type of use, such as domestic use, may be preferred over others when there are competing applications to appropriate the same water. Persons having water rights for preferred use may be entitled to take water before those having rights for other uses, regardless of their relative priorities. A person needing water for a preferred use may be authorized to condemn (i.e., to buy in a forced judicial sale) water being used for non-preferred purposes.

PRESCRIBED WATER RIGHTS — Water rights to which legal title is acquired by long possession and use without protest of other parties. Contrast with Appropriative Water Rights, Riparian Water Rights, and Littoral Water Rights.

PRESCRIPTIVE WATER RIGHTS — Water rights which are acquired by diverting water and putting it to use in accordance with specified procedures, e.g., filing a request with a state agency to use unused water in a stream, river, or lake.

PRESEDIMENTATION — (Water Quality) A pretreatment process used to remove gravel, sand, and other gritty material from raw water before it enters the main treatment plant. This is usually done without the use of coagulating chemicals.

PRESERVATION — The natural resources policy that stresses the aesthetic aspects of forests, rivers, wetlands, and other areas and tends to favor leaving such areas in an undisturbed state.

PRESSURE — Force per unit area. Enclosed fluids exert a force perpendicular to the surface of the containing vessel. The shape of the container does not affect the fluid pressure.

PRESSURE FILTER — (Water Quality) A device used to remove fine particulate matter from water. The filter consists of a filter medium, such as sand or anthracite coal, packed in a watertight vessel.

PRESSURE FILTRATION — (Water Quality) A process by which liquid is removed from a sludge by using external pressure to force it through a filter.

PRESSURE GAGE — An instrument, graduated in any units desired, for registering the pressure of solids, liquids, or gases.

PRESSURE GRADIENT — The change in pressure with distance, from lower to higher pressure, or vice versa.

PRESSURE HEAD — The relative pressure (excess over atmospheric pressure) divided by the unit weight of water; expressed in units of height.

PRESSURE RELIEF PIPES — Pipes used to relieve uplift or Pore Pressure in a dam foundation or in the dam structure.

PRESSURE SEWERS — A system of pipes in which water, wastewater, or other liquid is pumped to a higher elevation.

PRESSURE, STATIC — Pressure exerted by a fluid at rest.

PRIMARY DATA — (Data Analysis) Typically, data acquired by direct interaction, such as direct observation through measurements, tabulation, or surveys. Contrast with Secondary Data.

PRIMARY SETTLING TANK — (Water Quality) A holding tank where raw sewage or other wastewater is retained to allow the settling and removal of particulate material. The material that separates from the suspension is often termed Sludge.

PRIMARY SLUDGE — The Sludge produced by primary treatment in a wastewater treatment plant.

PRINCIPAL SPILLWAY — Allows discharge of water from a reservoir when the water level exceeds the top of the spillway. Principal spillways are used to allow small inflows to be released from the reservoir.

PRIOR APPROPRIATION DOCTRINE — The system for allocating water to private individuals used in most Western states. The doctrine of Prior Appropriation was in common use throughout the arid west as early settlers and miners began to develop the land. The prior appropriation doctrine is based on the concept of "First in Time, First in Right". The first person to take a quantity of water and put it to Beneficial Use has a higher priority of right than a subsequent user. Under drought conditions, higher priority users are satisfied before junior users receive water. Appropriative rights can be lost through nonuse; they can also be sold or transferred apart from the land. Contrasts with Riparian Doctrine and Riparian Water Rights.

PRIORITY — The concept that the person first using water has a better right to it than those commencing their use later. An appropriator is usually assigned a "priority date". However, the date is not significant in and of itself, but only in relation to the dates assigned other water users from the same source of water. Priority is only important when the quantity of available water is insufficient to meet the needs of all those having a right to use water.

PRIORITY DATE — The date of establishment of a water right. The rights established by application have the application date as the date of priority.

PROBABLE MAXIMUM FLOOD (PMF) — The largest flood for which there is any reasonable expectancy in a particular climatic era.

PROBABLE MAXIMUM PRECIPITATION — The maximum amount of precipitation for a given period that can reasonably be expected to occur in a specific drainage basin.

PROCESS WASTEWATER — Any water that comes into contact with any raw material, product, byproduct, or waste.

PROCESS WATER — Any water that comes in contact with a new material or product. The water is often released as wastewater following use.

PRODUCED WATER — As crude oil is extracted from a well, the water that comes to the surface with the oil. The produced water can constitute a large fraction of the total fluids extracted, and it is either pumped back into an underground formation via an Injection Well or discharged to surface water.

PRODUCT WATER — Output water of a desalting or water treatment plant.

PROFILE — A graph showing variation of elevation with distance along a traverse or profile cross section.

PROFUNDAL ZONE — The deep, bottom-water area beyond the depth of effective light penetration. Includes all the lake floor beneath the Hypolimnion.

PROJECT CROP WATER REQUIREMENT — The project crop water requirement is the annual amount of water required to meet the total project's crop consumptive use plus leaching requirement, and adjusted for natural precipitation (expressed in acre-feet per year).

PROJECT EFFICIENCY — The project efficiency is a general term referring to the efficiency relating to all aspects of a project's use of water.

PROJECT EVALUATION PERIOD — Expected useful life of a project beginning at the end of the installation of the project.

PROJECT YIELD — The water supply attributed to all features of a project, including integrated operation of units that could be operated individually. Usually, but not always, it is the same as the firm water yield.

PSYCHROMETER — A Hygrometer used to determine relative humidity of the atmosphere. It usually consists of two thermometers, one wet and one dry bulb, with the wet bulb wrapped in a cloth wick saturated with water which, due to evaporation, causes the temperature to fall below that of the air. From this difference in temperature and the use of specially prepared tables, the relative humidity can be determined.

PUBLIC WATER USE — Water supplied from a Public Water Supply System and used for such purposes as fire fighting, street washing, and municipal parks and swimming pools. Public water use also includes system water losses (water lost to leakage) and brine water discharged from desalination facilities.

PUMP — A device which moves, compresses, or alters the pressure of a fluid, such as water or air, being conveyed through a natural or artificial channel.

PUMP (HEAD) CURVE — The relationship between the head developed by a pump and the capacity (flow) for a constant rotative speed.

PUMP LIFT — The distance between the ground water table and the overlying land surface.

PUMPED HYDROELECTRIC STORAGE — Storing water for future use in generating electricity. Excess electrical energy produced during a period of low demand is used to pump water up to a reservoir. When demand is high, the water is released to operate a hydroelectric generator.

PUMPED STORAGE — (1) A reservoir that has a pumping plant as the main source of water supply. (2) Water pumped upgrade into a reservoir or lake during periods of low electric power consumption. The water added to the reservoir is later released through the hydroelectric facility to generate electricity during times of high power demand.

PUMPED STORAGE PLANT — A hydroelectric power plant which generates electric energy for peak load use by utilizing water pumped into a storage reservoir during off-peak periods.

PUMPED STORAGE PROJECT — A hydroelectric power plant and reservoir system using an arrangement whereby water released for generating energy during peak load periods is stored and pumped back into the upper reservoir, usually during periods of reduced power demand.

PUMPING-GENERATING PLANT — A plant at which the turbine-driven generators can also be used as motor-driven pumps.

PUMPING HEAD — Energy given to a fluid by a pump; usually expressed in feet of fluid (foot-pounds per pound).

PUMPING STATION — Mechanical devices installed in sewer or water systems or other liquid-carrying pipelines to move the liquids to a higher level.

PUMPING TEST — A test that is conducted to determine aquifer or well characteristics. More specifically, a test made by pumping a well for a period of time and observing the change in Hydraulic Head in the aquifer. A pump test may be used to determine the capacity of the well and the hydraulic characteristics of the aquifer.

PURIFICATION (Water) — Steps taken to eliminate impurities and pollution from water.

PURIFICATION PROCESS (Water) — The sequence of steps taken, beginning with unpurified water, which results in purified water delivered through a water system to the ultimate consumer. This sequence would normally include most or all of the following:
[1] Begin with unpurified water;
[2] Screening — removal of leaves, sticks and large foreign material;
[3] Pre-Chlorination — removal of disease organisms, bad taste, and odors;
[4] Pre-Settling — settling out large dirt particles;
[5] Flash Mix — a process in which chemicals are added to cause fine dirt to clump together;
[6] Coagulation/Flocculation — a process in which flash mix particles are gathered and made even larger;
[7] Sedimentation — a process in which gravity is used to settle out the large particles formed in coagulation/flocculation;
[8] Filtration — removal of any remaining particles; water is at least 99 percent particle-free at this point in the process;
[9] Final Chlorination — removal of any remaining disease organisms and adds necessary chlorine to prevent microbe regrowth in the distribution system;
[10] Corrosion Control — a step in which chemicals are added to neutralize the corrosive effects of "soft" water systems, thereby preventing damage to plumbing and fixtures;
[11] Finally, effluent pumps send the purified water to residential, commercial, and industrial establishments.

PURIFY (Water) — To rid water of impurities or pollution.