Appropriation and priority, beneficial use and forfeiture, general stream adjudications, transfers and injury to other users, irrigation and conservancy districts, groundwater management and conjunctive use, and interstate compacts.
Most western states allocate groundwater by appropriation, while others apply absolute ownership, reasonable use or correlative rights. Where levels decline or wells interfere, a state agency may designate a management area after study and hearing. Designation supports a moratorium on new permits, well spacing, metering, allocations stated per irrigated acre, and scheduled reductions.
Rivers crossing state lines are divided in three ways: a compact negotiated by the states and consented to by Congress, an equitable apportionment decreed by the Supreme Court, or an apportionment enacted by statute. A consented compact becomes federal law and cannot be altered by one state. Enforcement lies in the Court's exclusive original jurisdiction over controversies between states.
A water right can be lost in two ways that are routinely confused. Abandonment is a common law doctrine requiring both nonuse and an intent to relinquish, proved by the party asserting it, with prolonged nonuse serving as evidence of intent rather than as a substitute for it. Forfeiture is statutory and operates on nonuse alone for a fixed term, commonly five years, subject to statutory excuses and to a declaration procedure with notice and a right to be heard.
Instream flow rights protect water left in a channel for fish, wildlife, recreation or water quality. Because the classical doctrine required a diversion, these rights exist only by statute. Most states allow only a designated agency to hold them, cap the quantity at the minimum needed, tie the right to a defined reach, and forbid injury to existing appropriations.
A holder may apply to change the point of diversion, place of use, purpose of use or season of a water right, keeping the original priority date. Approval depends on the no-injury rule: no other vested right may be diminished in quantity, timing or quality. The transferable amount is limited to historical consumptive use computed over a representative period, and return flows must be replicated in amount, timing and location. Applications are published, protested and approved with conditions.
A general stream adjudication is a comprehensive proceeding, judicial in most states, that determines every right to the use of water from a source and enters a decree ranking them by priority. All claimants must be joined, and the United States may be joined under the McCarran Amendment where a comprehensive adjudication is under way. A claimant who fails to file a statement of claim by the court's deadline generally forfeits the claim, whatever the underlying history of use.
Under prior appropriation a water right is created by diverting water and applying it to a beneficial use, with a priority ranked by the date the effort began. Nearly every western state now administers the doctrine through a permit issued by a state engineer or equivalent officer. In shortage there is no proration: a senior may place a call and junior users are curtailed in reverse order of priority until the senior right is satisfied. Water law is state law, and the details differ.
Western codes make beneficial use the basis, the measure and the limit of a water right. A holder may divert no more than the use reasonably requires, and the allowance for irrigation is set by a duty of water expressed in volume per acre or flow per acre. Diversion beyond need, or by unreasonable means, is waste and may be curtailed. Water saved through efficiency generally returns to the stream rather than becoming the appropriator's to sell, subject to state conservation statutes.
An irrigation district is a special-purpose political subdivision formed by landowner petition and election, governed by an elected board, and financed by assessments levied on land within its boundaries and collected with the force of a tax lien. The district ordinarily holds the water right and owes landowners ratable delivery of available supply rather than a guaranteed quantity.
Groundwater hydraulically connected to a stream is administered together with surface rights in most appropriation states. Pumping captures streamflow, but the effect arrives on a lag of months, years or decades, so curtailing a junior well may deliver nothing to the calling senior this season. States respond by classifying groundwater, approving augmentation plans that supply substitute water when depletions occur, and curtailing only where it will help.
When the United States withdraws land from the public domain and reserves it for a federal purpose, it impliedly reserves water then unappropriated in the amount necessary to accomplish that purpose. The priority dates from the reservation, not from any diversion, and the right is not lost through nonuse. The doctrine reaches groundwater as well as surface water but is confined to the primary purposes of the reservation; secondary purposes must be served by appropriation under state law.
