Dotted termshave plain-English definitions. Hover, or tap on a phone.
Glossary
Keep this open on a second screen for the first few reads. Terms are grouped by where you’ll hit them.
Units and measurement
| Term | Definition |
|---|---|
| Acre-foot (AF) | Volume covering 1 acre to 1 foot deep. 325,851 gallons. Roughly 2 to 3 suburban households per year. The standard unit of western water. |
| Acre-foot per year (AFY) | Annual volume entitlement. |
| Cubic feet per second (cfs) | Flow rate. 1 cfs running for 24 hours is about 1.98 acre-feet, so “1 cfs for a day is about 2 acre-feet” is a useful shortcut. |
| Gallons per minute (gpm) | Well capacity. A household well is typically 5 to 15 gpm. Arizona’s non-exempt threshold is 35 gpm. |
| MGD | Million gallons per day. The unit for municipal supply and Great Lakes diversions. |
| Consumptive use | Water withdrawn and not returned to the source: evaporated, transpired by plants, embedded in product. The number that actually matters. |
| Return flow | Water withdrawn and returned to the system. Downstream users depend on it, which is why you generally can’t sell it. |
| Static water level | Depth to water in a well at rest. Its multi-decade trend is the single best indicator of aquifer health. |
| Drawdown | Drop in water level caused by pumping. |
| Cone of depression | The funnel-shaped drawdown around a pumping well. Overlapping cones are why neighbors’ wells interfere. |
Doctrine
| Term | Definition |
|---|---|
| Usufructuary right | A right to use something you don’t own. Nearly all water rights are this. |
| Riparian rights | Rights held by owners of land touching a watercourse. Eastern rule. Wisconsin’s rule. |
| Littoral rights | Same idea, for land touching a lake or sea rather than a flowing stream. Often used interchangeably with riparian. |
| Prior appropriation | First in time, first in right. Western rule. Priority date controls in shortage. |
| Beneficial use | The productive use that creates and limits an appropriative right. “The basis, the measure, and the limit.” |
| Priority date | The date a right’s seniority attaches. The most valuable number in a western water deal. |
| Senior / junior | Relative position in the priority queue. Seniors are made whole before juniors get anything. |
| Call on the river | A senior right holder demanding that juniors stop diverting. |
| Appurtenant | Attached to and traveling with the land. Riparian rights are appurtenant, which is why they generally can’t be sold separately. |
| Correlative rights | Proportional sharing among overlying owners. California’s groundwater rule. |
| Absolute dominion / rule of capture | Pump freely, no liability to neighbors. English rule. Texas keeps it. |
| Reasonable use | Use is lawful until it unreasonably harms another’s use. Wisconsin’s groundwater rule after Michels Pipeline (1974). |
| Public trust doctrine | The state holds navigable waters and their beds in trust for the public and can’t abdicate that trust. Constitutional in Wisconsin. |
| Reserved (Winters) rights | Water implicitly reserved when the US set aside land. Senior priority, never lost by non-use. |
| Equitable apportionment | Supreme Court division of an interstate river. High evidentiary bar. |
| Prescriptive right | A right acquired by open, hostile, continuous adverse use for the statutory period. Rare in water and disfavored. |
Administration and transactions
| Term | Definition |
|---|---|
| Adjudication | Comprehensive court proceeding determining all rights on a stream system. Arizona’s Gila adjudication started in 1974 and is unfinished. |
| Decree | The court order establishing quantities and priority dates in an adjudication. |
| Perfected right | A right fully established by actual beneficial use, not merely applied for. |
| Abandonment | Loss of a right through non-use plus intent to abandon. |
| Forfeiture | Statutory loss through non-use for a set period, commonly 5 years, regardless of intent. |
| No-injury rule | A transfer can’t harm other right holders. The main constraint on water markets. |
| Historical consumptive use | The transferable portion of a right, usually much smaller than the face amount. |
| Change of use application | State approval to alter purpose, place, or point of diversion. Slow, contested, often shrinks the right. |
| Buy and dry | Purchasing farmland to retire the acreage and move its water to a city. Politically radioactive in rural areas. |
| Water ranching | Same practice, usually by an investor rather than a utility. |
| Virtual water | Water embedded in a traded commodity. Exporting alfalfa exports the water that grew it. |
Wisconsin and Great Lakes specific
| Term | Definition |
|---|---|
| OHWM (Ordinary High Water Mark) | The physical line marking the limit of the state’s trust title on navigable water. Private title runs to it. Determined by DNR from soil and vegetation evidence, not from your deed. |
| Navigable in fact | Wisconsin’s navigability test. Broadly, capable of floating a small recreational craft on a regularly recurring basis. |
| High capacity well | Wisconsin: capacity of 100,000 gallons per day or more, aggregated across all wells on a property. Requires DNR approval under Wis. Stat. 281.34. |
| Chapter 30 permit | DNR authorization for structures or activity on navigable waters: piers, dredging, riprap, grading near the OHWM. |
| Shoreland zoning | County-administered land use controls within 1,000 feet of a lake or 300 feet of a river, under Wis. Stat. 59.692 and NR 115. |
| Great Lakes Compact | The 2008 interstate compact, consented to by Congress, barring most diversions out of the Great Lakes basin. Federal law. |
| Diversion | Moving water out of the Great Lakes basin. Banned with narrow exceptions. |
| Straddling community | A municipality partly inside and partly outside the basin. Eligible for a diversion with state approval. |
| Community in a straddling county | Wholly outside the basin but in a county the basin line crosses. Needs unanimous approval from all 8 governors. Waukesha is the only one ever approved. |
| Return flow requirement | Compact condition that diverted water be treated and returned to the basin. The doctrine’s teeth. |
| Basin line | The surface watershed divide separating water draining to the Great Lakes from water draining elsewhere. In southeast Wisconsin it runs through developed suburbs, which is why it’s a live political line. |
| BRRTS | Wisconsin DNR’s Bureau for Remediation and Redevelopment Tracking System. The contaminated sites database you search before buying anything. |
| CAFO | Concentrated Animal Feeding Operation. Regulated large livestock facility. The manure and nitrate source in most Wisconsin groundwater disputes. |
| Karst | Fractured carbonate bedrock with thin soil. Surface contaminants reach the aquifer fast. Common in northeast Wisconsin. |
| Central Sands | Sandy central Wisconsin region with intense irrigated agriculture and the state’s most contested groundwater drawdown. |
Arizona specific
| Term | Definition |
|---|---|
| AMA (Active Management Area) | Arizona groundwater management zone with metering, reporting, pumping rights, and conservation requirements. 8 as of January 2026. |
| INA (Irrigation Non-Expansion Area) | Lighter-touch zone that freezes irrigated acreage without full AMA regulation. |
| Assured Water Supply | AMA rule requiring proof of 100 years of physically and legally available water before new subdivision approval. |
| Non-exempt well | Arizona: above 35 gpm, or irrigating more than 2 acres. Subject to metering inside an AMA. |
| Groundwater transportation basin | Statutorily designated basins from which groundwater may be moved to an AMA. Butler Valley is one, which is why Fondomonte’s leases there were politically explosive. |
| CAP (Central Arizona Project) | The 336 mile canal delivering Colorado River water to Phoenix and Tucson. Junior to California, so it takes the first cuts in shortage. |
| Subsidence | Permanent ground surface collapse from aquifer compaction after over-pumping. Destroys storage capacity irreversibly. |
Federal
| Term | Definition |
|---|---|
| Dormant Commerce Clause | The rule that states can’t unduly burden interstate commerce even absent federal legislation. Sporhase (1982) applied it to groundwater, which is why states can’t flatly ban water exports. |
| Equal footing doctrine | New states take title to navigable waterbeds at statehood on the same terms as the original 13. |
| McCarran Amendment | 1952 statute waiving federal sovereign immunity so federal and tribal water rights can be adjudicated in state general stream adjudications. |
| Compact | Interstate agreement approved by Congress. Becomes federal law and preempts conflicting state law. |
Research demo, not legal advice. Facts current as of July 2026. Water law is state-specific and moves quickly, so confirm anything you plan to act on with a licensed attorney and the relevant state agency.