Resources

Water Right

A legal authorization to divert and use public water for a defined beneficial use. Water rights in Idaho are granted as:

Permits (provisional rights being developed)
Licenses (rights confirmed after development)
Decrees (court-validated rights issued through adjudication)

Adjudication

A judicial process, coordinated with IDWR (Idaho Department of Water Resources), used to verify and decree all existing water rights within a drainage basin.

Decree

A formal court order that defines a water right’s priority, amount, location, and allowable use.

Beneficial Use Doctrine

A constitutional principle that guides Idaho’s water management. While the prior appropriation doctrine gives preference to older rights, water must also be put to its most beneficial use in the public interest.

Forfeiture Exceptions

There are several exceptions to the forfeiture rule, set forth in Idaho Code 42-223. An important exception is that water rights that are not used in accordance with an approved mitigation plan are not subject to forfeiture.

Call/Delivery Call

A formal request by a senior water user for water administration to curtail junior water users when there is insufficient supply. See IDAPA 37.03.11.

Futile Call

Occurs when curtailing a junior right would not help satisfy a senior right. In such cases, the curtailment is not ordered.

Appropriation Date

See Priority Date.

Instream Flow Water Right

A non-diverted right to maintain water in a stream for public or ecological benefit.

De Minimis Use

A domestic or stockwater use not exceeding 13,000 gallons/day. See Idaho Code 42-111.

Water Right Elements

Each water right includes:

POU (Place of Use) The land or location where water is applied.
POD (Point of Diversion) Where water is diverted from its natural course.
Priority Date Establishes seniority—older rights are served first in shortage.
Use Type, Volume, and Rate How much water can be diverted (volume in acre-feet, flow rate in CFS), for what purpose, and during what timeframe.

Beneficial Use

Water must be put to a useful purpose to maintain a right. Examples include irrigation, domestic use, commercial, industrial, stock watering, etc.

Forfeiture

When a water right is not used for a specified period (usually 5 years), it may be subject to forfeiture—unless non-use is for a legally protected reason.

Priority Date/Appropriation Date

The date when a water right was legally established. During shortages, water is distributed based on these dates—"first in time, first in right."

Curtailment

When IDWR restricts or reduces water use based on priority. Junior rights may be shut off to satisfy seniors.

Injury

Harm or deprivation caused to a senior water right holder when they do not receive their full legal allocation.

Evapotranspiration

Water loss to the atmosphere through evaporation and plant transpiration.

Instream Livestock Water Right

The right to water livestock directly from a stream.

Prior Appropriation Doctrine

The legal system of “first in time, first in right.”

Acre-Foot (AF)

A unit of volume equal to one acre of land covered one foot deep with water. Equivalent to 325,851 gallons.

Diversion

The act of removing water from its natural course (stream, aquifer, etc.) for use.

Return Flows

Water that returns to rivers or streams after use (e.g., irrigation runoff).

Drawdown

The lowering of a water level in a reservoir or aquifer due to water release or pumping.

Mitigation/Mitigation Plan

Actions designed to prevent or offset injury to senior water users by junior groundwater use. Mitigation plans are submitted to and approved by IDWR and must identify specific remedies. See IDAPA 37.03.11.

CFS (Cubic Feet Per Second)

A measure of water flow rate. One CFS equals about 448.8 gallons per minute.

Non-Consumptive Use

Use that doesn’t deplete the water source (e.g., recreation, aesthetics).

Depletion

The amount of water permanently lost to a water system after use.

Recharge

The process of returning water to an aquifer via natural infiltration or artificial means (e.g., recharge basins or injection wells).

Telemetry

Telemetry refers to the use of technology to remotely monitor and transmit water measurements.

Aquifer

A geological formation that stores groundwater:

Tributary Aquifer: Hydrologically connected to surface water.
Non-Tributary Aquifer: Isolated from surface water.

Groundwater

Water beneath the surface of the earth. Often accessed via wells.

Storage Water

Water held in reservoirs or artificially impounded for later use.

Watershed/Basin

A geographic region where all precipitation drains into a common water body.

Basin: Typically defined by a major river.
Watershed: Includes all surface and subsurface flow paths.

Minimum Stream Flow

A legal minimum flow required to maintain ecological and recreational values. These limits override junior water rights.

Eastern Snake Plain Aquifer

The Eastern Snake Plain Aquifer is Idaho’s largest water source, stretching across 10,800 square miles and 16 counties. Beneath the surface, it contains an estimated 1 billion acre-feet of water, roughly equivalent to the fourth-largest Great Lake, Lake Erie. This makes it one of the most productive aquifers in the world, and the lifeblood of Idaho.

Surface Water

Water visible on the earth’s surface—streams, rivers, lakes, and reservoirs.

Reservoir

A man-made or natural lake used to store water for irrigation, recreation, or flood control.

Tributary

Smaller streams or rivers that feed into a larger stream, river, or body of water. Tributaries contribute water to the basin.

Check Structure / Head Gate

Devices used to control the flow and direction of water through canals and ditches.

Injection Well

A well used to pump water directly into an aquifer for recharge purposes.

Lateral

A smaller ditch or channel that distributes water from a main canal to fields or users.

Drip Irrigation

A water-efficient method of irrigation that slowly applies water to plant roots.

Water Right Administration

Water distribution under Idaho’s prior appropriation doctrine is enforced by IDWR via Water Districts and Watermasters who monitor and regulate water diversions. For groundwater, IDWR uses critical groundwater areas and ground water management areas to regulate water diversions.

Conjunctive Management

A regulatory approach to manage surface and groundwater together, recognizing their hydraulic connection and aiming to maximize use of both.

Groundwater District

A district formed by groundwater users to manage water rights and collectively address groundwater issues.

Watermaster

Oversees water distribution in a water district under Idaho water law and the prior appropriation doctrine. Each water district has a Watermaster appointed by IDWR, who is elected and paid by district water users.

Idaho Department of Water Resources (IDWR)

The state agency charged with regulating the use of Idaho water rights.

Irrigation District

A public organization that delivers water to landowners through canals and pipelines, primarily for agriculture.

Canal Company

A private or shareholder-based entity that operates and maintains irrigation delivery systems and diverts water on behalf of its users.