A Guide to Water Terms


See "Water Quality Terms and Definitions" web page for additional words and phrases.


acequia -- gravity-driven waterways; most are simple ditches with dirt banks, but they can be lined with concrete.

acre-foot (acre-ft) -- An acre-foot is the unit used to measure large volumes of water such as reservoirs and aqueducts. It is defined as the amount of water required to cover 1 acre of land (approximately the size of a football field) to a depth of 1 foot and is equal to 325,851 gallons. The average family in Tucson uses one quarter acre-foot of water per year.

aerator -- a device screwed onto the end of a faucet spout that mixes air into flowing water to reduce water flow.

aqueduct -- a pipe, conduit, or channel designed to transport water from a remote source, usually by gravity.

aquifer -- An aquifer is a naturally-occurring rock or sediment basin that stores water. This water can be pumped out for delivery to customers. Tucson’s water supply is stored in the Tucson/Avra Valley Aquifer.

aridification -- a period of transition to an increasingly water scarce environment—an evolving new baseline around which future extreme events (droughts and floods) will occur.

artificial recharge -- a process where water is put back into groundwater storage from surface-water supplies such as irrigation, or induced infiltration from streams or wells.


backflow -- flow of water in a pipe or line in a direction opposite to the normal flow. A backflow prevention assembly prevents non-potable water from being drawn into the public drinking water system.

bedrock -- the solid rock beneath the soil and superficial rock; a general term for solid rock that lies beneath soil, loose sediments, or other unconsolidated material.

blended water -- a blend of Central Arizona Project water (from the Colorado River) and groundwater delivered to Tucson Water customers. The current blend is 95% CAP, 5% groundwater.

booster pump -- a pump that is used to move water uphill.


Ccf -- one hundred cubic feet (Ccf); the unit of measurement for billing for water use. One cubic foot (cf) of water is 7.48 gallons; one hundred cubic feet (Ccf) of water is equal to 748 gallons of water.

condensation -- the process of water vapor in the air turning into liquid water. Condensation is the opposite process of evaporation.

consumptive use -- the part of water withdrawn that is evaporated, transpired, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment.

conveyance loss -- water that is lost in transit from a pipe, canal, or ditch by leakage or evaporation.

cubic feet per second (cfs) -- a rate of the flow equal to a volume of water one foot high and one foot wide flowing a distance of one foot in one second. One cfs is equal to 7.48 gallons of water.


desalination -- the removal of salts from saline water to provide freshwater.

discharge -- the volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second.

domestic water use -- water used for indoor household purposes such as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and outdoor purposes such as watering lawns and gardens.

drawdown -- a lowering of the groundwater surface caused by pumping.

drought -- Drought is a prolonged period of below-average precipitation severe enough to negatively impact the environment and human activities. Drought is a natural occurrence and Arizona is especially sensitive to drought, since water is scarce here even during average years. Population growth continues to increase demand for water. Drought can impact domestic water supplies, ranching and farming production, vegetation, forest health, and wildlife populations.

drought response stage -- a level of severity of drought response as measured by agreed-upon indicators. Tucson Water's Drought Response Plan has four stages.


effluent -- water that flows from a sewage treatment plant after it has been treated.

ephemeral -- used to describe a wetland, spring, stream, river, pond, or lake that only exists for a short period following precipitation or snowmelt.

erosion -- the process in which a material is worn away by a stream of liquid (water) or air, often due to the presence of abrasive particles in the stream.


filtration -- the process of running water through various substances that strain out harmful bacteria or chemicals. The earth acts as a natural filter as water runs through it. Sand and charcoal filters achieve the same thing, but more quickly.

flood stage -- the elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured.


gray water -- wastewater from clothes washing machines, showers, bathtubs, hand washing, lavatories and sinks that can be used to water landscapes.

groundwater -- (1) water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturated zone is called the water table. (2) Water stored underground in rock crevices and in the pores of geologic materials that make up the Earth's crust.

groundwater basin -- an area enclosing a relatively distinct hydrologic body or related bodies of groundwater.


hardness -- a water-quality indication of the concentration of alkaline salts in water, mainly calcium and magnesium.

hydrologic cycle -- the cyclic transfer of water vapor from the Earth's surface via evapotranspiration into the atmosphere, from the atmosphere via precipitation back to earth, and through runoff into streams, rivers, and lakes, and ultimately into the oceans.


indicator -- a variable that changes as drought conditions change.

infiltration -- flow of water from the land surface into the subsurface.

injection well -- refers to a well constructed for the purpose of injecting treated wastewater directly into the ground. Wastewater is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into aquifers that don't deliver drinking water, unused aquifers, or below freshwater levels.

irrigation -- the controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall.

isolated system -- An isolated system is a small water system that may serve fewer than 25 people or up to 10,000 people. An isolated system has its own source or well, and an independent distribution system. It may also have a water treatment facility.


million gallons per day (mgd) -- a rate of flow of water equal to 133,680.56 cubic feet per day, or 1.5472 cubic feet per second, or 3.0689 acre-feet per day. A flow of one million gallons per day for one year equals 1,120 acre-feet (365 million gallons).

municipal water system -- a water system that has at least five service connections or which regularly serves 25 individuals for 60 days; also called a public water system.


osmosis -- the movement of water molecules through a thin membrane. The osmosis process occurs in our bodies and is also one method of desalinating saline water.

overdraft -- using groundwater faster than nature can replenish it.


pH -- 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.

per capita use -- Also known as gallons per capita per day (GPCD), this is the average amount of water each person in a particular area uses on a daily basis. One way to determine per capita demand is to measure the amount of potable water delivered in one year, divide that number by the total population in the water service area, and divide that number by 365 days. In 2018, Tucsonans’ residential water use was 80 GPCD, the amount of water a standard bathtub holds.

percolation -- the movement of water through the openings in rock or soil that contributes to ground water replenishment.

permeability -- 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, don't allow water to flow freely.

potable -- (POE-tuh-bull): Water that is safe for drinking, bathing, and food preparation is referred to as potable water. It is free of contamination and meets all drinking water standards. The taste of potable water may vary due to its mineral content, hardness, temperature, etc. The word comes from the Latin word potare, meaning to drink.

precipitation -- As we have already seen in Tucson this year, precipitation comes in many forms including rain, snow, hail, dew, and frost. According to the National Geographic Society, precipitation is any type of water that forms in the Earth's atmosphere and then drops onto its surface.

purified water -- water that is mechanically filtered or processed to be cleaned for consumption.


recharge -- Recharge happens when water moves into an aquifer. Natural recharge is caused by precipitation that results in water moving from a mountain front, lake, or stream into an aquifer. Artificial recharge can be done by spreading basins, injection wells, or diversion projects. Incidental recharge is due to other activities such as farming. Understanding and quantifying these processes are critical to water resources management.

reclaimed water -- treated wastewater that can be used for beneficial purposes, such as irrigation.

recycled water -- water that is used more than one time before it passes back into the natural hydrologic system.

reservoir -- a pond, lake, or basin, either natural or artificial, for the storage, regulation, and control of water.


safe yield -- a groundwater management goal which attempts to achieve and thereafter maintain a long-term balance between the annual amount of groundwater withdrawn in an Active Management Area and the annual amount of natural and artificial recharge within a designated area.

seepage -- (1) the slow movement of water through small cracks, pores, interstices, etc., of a material into or out of a body of surface or subsurface water. (2) The loss of water by infiltration into the soil from a canal, ditches, laterals, watercourse, reservoir, storage facilities, or other body of water, or from a field.

service area -- the area served by a municipal water provider.

shut-off valve -- two main types of shut-off valves are found in the home: (1) a gate valve, which opens by turning the handle left (counterclockwise) to start water flow and closes by turning it right (clockwise) to stop water flow. (2) a ball valve, which opens by turning the handle parallel to the water line to start water flow and closes by turning it perpendicular to the water line to stop water flow.

subsidence -- a dropping of the land surface as a result of ground water being pumped. Cracks and fissures can appear in the land. Subsidence is virtually an irreversible process.


transpiration -- process by which water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, such as leaf pores.

triggers -- the value or combined value of one or more indicators that cause a change from one drought response stage to another.

turbidity -- Turbidity is the measure of relative clarity of a liquid. The amount of solid particles suspended in water causes light rays shining through the water to scatter, making it cloudy or muddy. Excessive turbidity in drinking water is aesthetically unappealing, and may also represent a health concern. Following installation of a new well or repair of a water line, Tucson Water performs a thorough flush until the water clears. Note: water from a flush is typically directed into a stormwater drain or wash so it returns to the aquifer.


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

water cycle -- the circuit of water movement from the oceans to the atmosphere and to the Earth and return to the atmosphere through various stages or processes such as precipitation, runoff, percolation, storage, evaporation, and transportation, etc.

water efficiency -- Water efficiency means using the least amount of water necessary to carry out a task. This differs from water conservation because water efficiency focuses on reducing waste, not restricting use. Improve water efficiency in your home (and save money) by installing low-flow fixtures such as faucets and shower heads, and high-efficiency toilets and clothes washers. Tucson Water offers rebates for installing high-efficiency fixtures.

watershed -- the land area that drains water to a particular stream, river, or lake. This land feature can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Arizona, six other states, and Mexico are in the Colorado River Basin (watershed).

water table -- the top layer of the aquifer. As more groundwater is used, the water table lowers and drilling must go deeper to find water.


xeriscaping -- a method of landscaping that uses plants that are well-adapted to the local area and are drought-resistant.