Volume of water needed to cover 1 acre to a depth of 1 foot. It equals 325,851 gallons.


Geologic formation that contains sufficient saturated permeable material to yield significant quantities of water to wells and springs. The formation could be sand, gravel, limestone, sandstone, or fractured igneous rocks.


Maximum amount of water available during the drought of record, regardless of whether the supply is physically or legally available.

Brackish Water

Water with total dissolved solids between 1,000 and 10,000 milligrams per liter.

Capital Cost

Portion of the estimated cost of a water management strategy that includes both the direct costs of constructing facilities, such as materials, labor, and equipment, and the indirect expenses associated with construction activities, such as costs for engineering studies, legal counsel, land acquisition, contingencies, environmental mitigation, interest during construction, and permitting costs.

Conjunctive Use

The combined use of groundwater and surface water sources that optimizes the beneficial characteristics of each source.

County – Other

An aggregation of residential, commercial, and institutional water users in cities with less than 500 people or utilities that provide less than an average of 250,000 gallons per day, as well as unincorporated rural areas in a given county.


Process of removing salt from seawater or brackish water.


Term is generally applied to periods of less than average precipitation over a certain period of time. Associated definitions include meteorological drought (abnormally dry weather), agricultural drought (adverse impact on crop or range production), and hydrologic drought (below average water content in aquifers and/or reservoirs).

Drought Of Record – DOR

Period of time during recorded history when natural hydrological conditions provided the least amount of water supply. For Texas as a whole, the drought of record is generally considered to be from about 1950 to 1957.


Bay or inlet, often at the mouth of a river, in which large quantities of freshwater and seawater mix together.

Existing Water Supply

Maximum amount of water available from existing sources for use during drought of record conditions that is physically and legally available for use.

Firm Yield

Maximum water volume a reservoir can provide each year under a repeat of the drought of record.

Flood Control Storage

Storage in a lake or reservoir, between two designated water surface elevations, that is dedicated to storing floodwater so that flood damages downstream are eliminated or reduced.

Freshwater Inflow Needs

Freshwater flows required to maintain the natural salinity and nutrient and sediment delivery in a bay or estuary that supports their unique biological communities and ensures a healthy ecosystem.

Groundwater Availability Model – GAM

Numerical groundwater flow models used by TWDB to determine groundwater availability of the major and minor aquifers in Texas.

Groundwater Management Area – GMA

Area designated and delineated by TWDB as an area suitable for management of groundwater resources.


Physical means for meeting water and wastewater needs, such as dams, wells, conveyance systems, and water treatment plants.

Instream Flow

Water flow and water quality regime adequate to maintain an ecologically sound environment in streams and rivers.

Interbasin Transfer

Physical conveyance of surface water from one river basin to another.

Major Reservoir

Reservoir having a storage capacity of 5,000 acre-feet or more.

Modeled Availalbe Groundwater – MAG

The total amount of groundwater, including both permitted and exempt uses, that can be produced from the aquifer in an average year, that achieves the desired future condition for the aquifer.


Projected water demands in excess of existing water supplies for a water user group or a wholesale water provider.

Planning Group

Team of regional and local leaders of different backgrounds and various social, environmental, and economic interests responsible for developing and adopting a regional water plan for their planning area at five-year intervals.


Amount of water that infiltrates to the water table of an aquifer.

Recommended Water Management Strategy

Specific project or action to increase water supply or maximize existing supply to meet a specific need.


Use of surface water that has already been beneficially used once under a water right or the use of groundwater that has already been used.

Run-Of-River Diversion

Water right permit that allows the permit holder to divert water directly out of a stream or river.

Safe Yield

The annual amount of water that can be withdrawn from a reservoir for a period of time longer than the drought of record.


Action or process of depositing sediment in a reservoir, usually silts, sands, or gravel.


Natural or artificial impoundment and accumulation of water in surface or underground reservoirs, usually for later withdrawal or release.

Subordination Agreement

Contracts between junior and senior water right holders where the senior water right holder agrees not to assert its priority right against the junior.

Unmet Needs

Portion of the demand for water that exceeds water supply after inclusion of all recommended water management strategies in a regional water plan.

Water Availability Model

Numerical surface water flow models to determine the availability of surface water for permitting in the state.

Water Demand

Quantity of water projected to meet the overall necessities of a water user group in a specific future year.

WUG Water User Group

Identified user or group of users for which water demands and water supplies have been identified and analyzed and plans developed to meet water needs. Water user groups are defined at the county level for the manufacturing, irrigation, livestock, steam-electric power generation, and mining water use categories. Municipal water user groups include (a) incorporated cities and selected Census Designated Places with a population of 500 or more; (b) individual or groups of selected water utilities serving smaller municipalities or unincorporated areas; and (c) rural areas not included in a listed city or utility, aggregated for each county.

Wholesale Water Provider

Person or entity, including river authorities and irrigation districts, that had contracts to sell more than 1,000 acre-feet of water wholesale in any one year during the five years immediately preceding the adoption of the last regional water plan.