Glossary/water dictionary

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particle size

The diameter, in millimeters, of suspended sediment or bed material. ^


A disease-producing agent; usually applied to a living organism. Generally, any viruses, bacteria, or fungi that cause disease.^

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.^

per capita use

The average amount of water used per person during a standard time period, generally per day.^


 The value below which a given percentage of observations in a group of observations fall. For example, the 20th percentile is the value below which 20% of the observations may be found.^


(1) The movement of water through the openings in rock or soil. (2) The entrance of a portion of the streamflow into the channel materials to contribute to groundwater replenishment.^


The ability of a material to allow the passage of a liquid, such as water through rocks. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas unpermeable material, such as clay, do not allow water to flow freely.^


A measure of the relative acidity or alkalinity of water. Water with a pH of 7 is neutral; lower pH levels indicate increasing acidity, while pH levels higher than 7 indicate increasingly basic solutions.^

pilot project

An early, usually small, project set up to gain experience for operating the actual project.^

point-source pollution

Water pollution coming from a single point, such as a sewage-outflow pipe.^


A measure of the water-bearing capacity of subsurface rock. With respect to water 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 because the pores are usually so small.^

portable flume (portable weir)

A portable flume for measuring small discharges, such as in farm laterals or watercourses, and consisting of a miniature broad-crested weir made of wooden or iron sheets.^

potable water

Water of a quality suitable for drinking.^

potentiometric surface / piezometric surface

"The imaginary line where a given reservoir of fluid will ""equalize out to"" if allowed to flow; a potentiometric surface is based on hydraulic principles."^


Rain, snow, hail, sleet, dew and frost.^

primary wastewater treatment

The first stage of the wastewater treatment process where mechanical methods, such as filters and scrapers, are used to remove pollutants. Solid material in sewage also settles out in this process.^

prior appropriation doctrine

"The system for allocating water to private individuals used in most Western US 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. The rights can be lost through non-use; they can also be sold or transferred apart from the land. Contrasts with 'riparian water rights'."^

public supply

Water withdrawn by public governments and agencies, such as a county water department, and by private companies that is then delivered to users. Public suppliers provide water for domestic, commercial, thermoelectric power, industrial and public water users. Most people's household water is delivered by a public water supplier. The systems have at least 15 service connections (such as households, businesses, or schools) or regularly serve at least 25 individuals daily for at least 60 days out of the year.^

public water use

Water supplied from a public-water supply and used for such purposes as firefighting, street washing, and municipal parks and swimming pools.^