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Water Lingo

Unfortunately, the water industry has utilized a variety of different terms, acronyms, units and descriptions over the last 170 years.  This can be confusing and complicate understanding water issues.  Water Lingo attempts to provide this key information with straightforward explanations with an emphasis on Arizona.

Common Terms

Active Management Area (AMA)-7 areas within Arizona with severe groundwater overdraft including the Tucson AMA.

Aquitard-an underground layer (usually clay) that impedes the migration of groundwater from one aquifer to another.

Arizona Department of Water Resources (ADWR)-regulates water supply in Arizona.

Arizona Water Banking Authority (AWBA) (1996)-stores excess CAP water (USF or GSF) for future use.

Aquifer-underground layer of water-bearing unconsolidated materials (gravel, sand or silt). 

Assured Water Supply (AWS)-water supply must be available to meet current and future water demands for 100 years.

Central Arizona Groundwater Replenishment District (CAGRD)(1993)-groundwater replenishment district managed by CAWCD.  Also manages the AWS program (1999).

Central Arizona Project (CAP)-336-mile long aqueduct system which distributes Arizona's Colorado River water allocation for the purpose of conserving groundwater. 

Central Arizona Water Conservation District (CAWCD)-water district (Maricopa, Pima and Pinal counties) formed to manage CAP and to repay the federal government for Arizona's share of CAP construction costs.  CAWCD also manages CAGRD.

Groundwater-water derived from an aquifer.

Groundwater Management Act (GMA)(1980)-groundwater legislation that covers groundwater permitting, storage and recovery.

Groundwater Recharge (Natural)-percolation of precipitation into an aquifer.

Groundwater Recharge (Artificial)-percolation or injection of non-groundwater water into an aquifer.  Also called Replenishment.

Groundwater Savings Facility (GSF)-an entity (usually a farm) that practices Indirect Recharge (In-Lieu Recharge).

Indirect Recharge (In-Lieu Recharge)-use of non-groundwater directly in-lieu of pumping groundwater, i.e. the groundwater that would have been pumped stays in the aquifer.

Injection Well-injects non-groundwater into the aquifer.

Law of the River-series of compacts, laws, court decisions, decrees, minutes (Mexico) and regulations that define Colorado River water rights.

Long Term Storage Credit (LTSC)-credit for groundwater storage whereby 1 LTSC=1 acre-foot of stored groundwater.

Maximum Contaminant Level (MCL)-the maximum allowed level of a substance in water usually expressed in milligrams per liter (mg/l) or micrograms per liter (ug/l).  See below.

Non-Groundwater-surface water (e.g. Colorado River water) or reclaimed (recycled) wastewater.

Overdraft-groundwater withdrawals exceed natural and artificial groundwater recharge (replenishment).

Prior Appropriation-Prior appropriation water rights (first in time, first in right) are determined by a priority system that gives the highest priority to the first user (senior appropriator) of the surface water. 

Reclaimed (Recycled) Wastewater-municipal wastewater that has been treated to a level allowed for groundwater recharge (replenishment) or turf irrigation.

Reasonable Use (Groundwater)-landowner can withdraw groundwater to make reasonable use of the landowner’s property and adjacent landowners have no claim if the groundwater under the adjacent landowner’s land is adversely impacted.

Recovery Well-well/pump installed near USF to recover recharged (replenished) groundwater.

Reserved Rights Doctrine-establishes that public land and tribal land set aside by the federal government have a reserved right to an adequate water supply.

Riparian-Riparian water rights are surface water rights inured to landowners that own property that touch a surface water, i.e. stream, river, etc.

Spreading Basin-large basin located at the ground surface that stores and percolates non-groundwater into the aquifer.

Sub-basin-a smaller portion of a Watershed (Drainage Basin).

Subsidence-settling of the ground surface related to subsurface geologic formation consolidation by excessive groundwater overdraft.


Surface Water-water derived from a lake, stream or river.

Underground Storage Facility (USF)-portion of an aquifer where non-groundwater recharge occurs via spreading basins or injection wells.


Water-the sustenance of life.

Watershed (Drainage Basin)-land area which drains towards a specific surface water.  

Well-long cylindrical steel casing installed in a vertical hole drilled in an aquifer. The bottom of the casing is screened to allow groundwater to enter the casing.

Well Pump-mechanical pump installed inside the well.  The pump can be Vertical Turbine (motor is above ground) or Submersible (motor is installed in the well and coupled directly to the pump).


Water volume is the unit used to measure how much water you use at your home/business, the capacity of a reservoir, etc.  The three key units are cubic feet, gallons and acre-feet.  These units are used for different purposes and are convertible.  Water meters can be purchased to read in cubic feet, gallons or acre-feet.


cubic feet (cf)

A cubic foot (cf) is simply a three-dimensional cube that is 1-foot long on each side.  If you fill the cube with water it will hold 7.48 gallons.  The conversion:


                        1 cf = 7.48 gallons  (actual conversion is 7.48052 but 7.48 is used for simplicity)

Cubic feet has been used primarily for domestic water meters.  To complicate things even further, most domestic water meters read in 100 cubic feet (ccf).  That would be 100 cubic foot cubes filled with water totaling 748 gallons.  The conversion:


                        1 ccf = 748 gallons


gallons (g)


Gallons is easiest for most of us to grasp because most familiar commodities are measured in gallons, e.g. milk, gasoline, etc.  Many water bills will convert the ccf meter readings to gallons so you can get a better understanding of how much water is used. 


Because many water resource facilities handle large amounts of water, the water industry uses million gallons (mg) when describing capacity.


acre-feet (af)


Large irrigation systems in the western United States use acre-feet due to the vast lands being irrigated.  One acre-foot is simply one acre of land covered by 1 foot of water and is equivalent to 325,851 gallons of water.  So, how did we get there:


            1 acre = 43,560 square feet or a square about 208.7 feet long by 208.7 feet wide


            1 acre-foot = 43,560 square feet x 1 foot = 43,560 cubic feet (cf)


            1 acre-foot = 43,560 cf x 7.48052 gallons/cf = 325,851 gallons

Another way to envision this is a football field (little over an acre) covered with 1-foot of water!

Volumetric Rate

Volumetric Rate is simply the volume of water in a given time period.  Some typical volumetric rates used in the water industry with examples are:



cubic feet per second (cfs)-the average flow in the Colorado River below Parker Dam is 13,400 cfs

gallons per day (gpd)-my average residential water use in February 2020 was 125 gpd

million gallons per day (mgd)-Pima County's Tres Rios Water Reclamation Facility treats 30 mgd of wastewater


Concentration is a measure of the amount of mass of substance in water. Here is where the units diverge to metric.  Instead of pounds of a substance in gallons of water, the water industry uses grams of a substance in liters of water.  Go figure!  More specifically the common units are:

milligrams per liter (mg/l) or parts per million (ppm)


1 mg/l = 1 mg in 1 liter of water 

To put this in perspective, 1 mg is a fraction of an ounce (0.000035274 ounces to be exact) and 1 liter is slightly more than a quart.  Analogy: 1 mg/l = 2 grains of salt in 1 liter of water!


The term parts per million (ppm) is used interchangeably with mg/l as they are equivalent terms

Example:  USEPA MCL for nitrate is 10 mg/l (as N)

micrograms per liter (ug/l) or parts per billion (ppb)

1 ug/l = 1 ug in 1 liter of water 

To put this in perspective:


1 ug = 1 mg/1,000 or even more of a fraction of an ounce (0.000000035274 ounces to be exact).  Analogy:  1 ug/l = 2 grains of salt in 1,000 liters (264 gallons) of water!


The term parts per billion (ppb) is used interchangeably with ug/l as they are equivalent terms

Example:  USEPA MCL for Selenium is 50 ug/l or 50 ppb


ug is used here as a common abbreviation for microgram but mcg is also used, especially for food supplements

Example:  My One A Day vitamin tablet contains 117 mcg of Selenium

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