Water Rights: Prior Appropriation, Riparian Doctrine, Groundwater, and Federal Reserved Rights

Summary. Two doctrines, one federal overlay, and the practical rules for getting, keeping, moving, and defending a water right.

Part I: Two systems

Every American water lawyer begins with the same fact: the country has two water doctrines, and they are opposites.

In the humid East, where rain is reliable, water rights attach to land adjoining the watercourse, are shared, and are measured by reasonableness. In the arid West, where rain is not, water rights are created by taking water and using it, are ranked by seniority, and are measured by priority.

The line falls roughly at the hundredth meridian, with a set of hybrid states in between that recognize both — typically honoring riparian rights established before a statutory date and applying appropriation thereafter.

And a third body of law sits above both: federal reserved rights, interstate allocation, and federal regulatory programs that constrain what anyone may do in or to a waterway regardless of who owns the water.

Part II: Riparian rights

The right belongs to the land. An owner of land abutting a watercourse has a right to make reasonable use of the water — a right that arises with ownership, is not created by use, and is not lost by non-use.

Reasonable use is relational. It is measured against the uses of other riparians, considering the purpose, suitability to the watercourse, economic and social value, harm caused, practicality of avoiding harm, and the burden of adjustment. No riparian has a fixed quantity; each has a right to a reasonable share, and in shortage all reduce together.

Consequences that follow:

Non-use does not forfeit. A riparian may begin using water after decades of not doing so.
Use off the riparian parcel is disfavored in the classical doctrine, and some states restrict transfers away from the watershed.
Domestic use is generally preferred over commercial and industrial use.
Natural flow ideas persist in some formulations, but modern doctrine is dominated by reasonable use.

Most riparian states have added a permit system, a "regulated riparian" model in which substantial withdrawals require a permit for a term, with conditions, reporting, and drought curtailment authority. The practical answer in an eastern state is therefore usually a statute, not the common law — but the common law still supplies the background rules and the litigation standard between neighbors.

Part III: Prior appropriation

"First in time, first in right." A water right is created not by land ownership but by diverting water and applying it to a beneficial use, and rights are ranked by the date the appropriation began.

The elements of an appropriative right:

Intent to appropriate.
Diversion from the source — though many states now recognize instream appropriations without a physical diversion.
Application to a beneficial use.
A priority date, generally relating back to the first step taken toward the appropriation if diligently completed.

Priority is the whole system. In shortage, the most senior right is satisfied in full before the next receives anything. There is no sharing and no proration. A right with an 1887 priority takes water while a right from 1954 receives none — and the 1954 right may be curtailed in a "call" made by the senior.

Beneficial use is the measure and the limit. A right exists only to the extent water is actually applied to a recognized beneficial use — irrigation, domestic, municipal, industrial, stock watering, power, recreation, and, increasingly, instream flow for fish and wildlife. Water beyond what the use requires is not part of the right.

Losing the right:

Abandonment requires non-use plus intent to abandon, with extended non-use often creating a presumption.
Forfeiture is statutory: non-use for a specified period — commonly five years — extinguishes the right regardless of intent, subject to statutory excuses.
"Use it or lose it" is the shorthand, and it is one reason water conservation has historically been penalized — a problem many states have addressed with conservation savings provisions.

Transfers and the no-injury rule. Appropriative rights are property and may be sold, leased, and moved — a market that is the central mechanism for reallocating water in the West.

But the transfer is limited to the historical consumptive use, not the paper right, and it may not injure other appropriators. Because irrigation return flows sustain downstream rights, moving a right upstream, changing its timing, or converting it to a fully consumptive use can injure juniors even where the diverted quantity is unchanged. Quantifying historical consumptive use is the central technical exercise in every transfer, and it is where transfers succeed or fail.

Part IV: Groundwater

Groundwater is governed separately, badly, and differently in nearly every state. Four doctrines recur:

Absolute dominion (the English rule). The overlying owner may pump without liability. Now rare in pure form.

Reasonable use (the American rule). Pumping must be for a reasonable use on the overlying land, with off-tract use restricted where it harms neighbors.

Correlative rights. Overlying owners share a common supply proportionally, with surplus available to others.

Prior appropriation, applied to groundwater in most western states, with permits, priority dates, and management areas.

The governing problem is that water does not respect the categories. Pumping from an aquifer connected to a stream depletes the stream, often with a delay of years or decades. Conjunctive management — regulating groundwater and surface water as one resource — is the modern approach, and it is contentious precisely because it subordinates junior groundwater pumpers to senior surface rights.

The recurring management tools: designated management areas or critical areas; permit moratoria; metering and reporting; pumping caps; well spacing; augmentation or replacement supply requirements, under which a pumper must replace depletions to the stream; and mitigation banking.

And a hard fact. Many aquifers are being mined — withdrawn faster than they recharge — which is a water-supply problem, a land-subsidence problem, and a legal problem, because the doctrines were built for a resource assumed to be renewable.

Part V: Federal reserved rights

When the United States reserves land — a reservation, a park, a forest, a monument — it implicitly reserves the water necessary to fulfill the purposes of the reservation.

The doctrine originates in Winters v. United States, which held that the establishment of an Indian reservation implicitly reserved water sufficient for its purposes — there, to convert a nomadic people to agriculture — and that the reservation's water right was not subordinated to later settlers' appropriations.

Three features make these rights extraordinary:

The priority date is the date of the reservation, which for many Indian reservations is very early — frequently senior to nearly every state-law right on the stream.
They are not lost by non-use. Neither abandonment nor forfeiture applies.
They are quantified by the purpose of the reservation, not by historical use. For agricultural reservations, Arizona v. California approved quantification by practicably irrigable acreage — the water needed to irrigate all land on the reservation that could practicably be irrigated.

The practical consequence is enormous. An unquantified reserved right hanging over a fully appropriated stream makes every junior right uncertain, which is why the dominant mode of resolution is now the negotiated Indian water rights settlement: the tribe accepts a quantified right, often less than a maximum legal claim, in exchange for federal funding for infrastructure, delivery, and sometimes economic development, with Congress ratifying the settlement.

Non-Indian federal reservations — parks, forests, monuments, wildlife refuges — also carry reserved rights, quantified more narrowly by the primary purposes of the reservation.

And the forum question. A federal statute permits joinder of the United States in comprehensive state general stream adjudications, and in Colorado River Water Conservation District v. United States the Supreme Court approved deference to such proceedings — a doctrine now used well beyond water law.

Part VI: Water between states

Three mechanisms allocate water among states:

Interstate compacts, negotiated among states and approved by Congress, which become federal law. Most major western rivers are governed by one, and compact interpretation disputes go to the Supreme Court's original jurisdiction.

Equitable apportionment, a federal common law doctrine under which the Court divides an interstate stream between states, weighing physical and climatic conditions, consumptive use, return flows, the character and rate of return, prior appropriations, and — importantly — the harm to the downstream state weighed against the benefit to the upstream state. Kansas v. Colorado established the doctrine's essentials.

Congressional apportionment, which is rare but available.

The recurring problem is that many compacts were negotiated using hydrology from unusually wet periods, allocating more water than the rivers reliably produce. The result is over-allocation on paper, resolved in practice by shortage-sharing agreements, drought contingency plans, and negotiated reductions — a process that is now continuous on several major systems.

Part VII: Adjudications

A general stream adjudication is a comprehensive judicial proceeding determining every water right on a stream system, its priority, its quantity, and its point and place of use.

They are enormous. Thousands of claimants, decades of duration, and a resulting decree that becomes the definitive record of rights on the system, administered thereafter by a watermaster.

If you receive notice of one, participate. A right not claimed in a general adjudication may be extinguished. This is the single most consequential piece of mail a water right holder can receive, and it is routinely ignored because it looks like a form letter.

Part VIII: The regulatory overlay

Owning a water right does not permit you to do whatever you like in a waterway.

The Clean Water Act, whose objective appears at 33 U.S.C. § 1251, prohibits the discharge of any pollutant from a point source into navigable waters except in compliance with a permit — the core prohibition at 33 U.S.C. § 1311. Discharges of dredged or fill material require a permit under 33 U.S.C. § 1344, which is what governs filling a wetland, building a dam, or altering a channel.

The jurisdictional question — what counts as "waters of the United States" — has been litigated for decades. United States v. Riverside Bayview Homes upheld jurisdiction over wetlands adjacent to navigable waters. Rapanos v. United States fractured, producing competing tests and years of confusion. And Sackett v. EPA substantially narrowed the reach, holding that the Act extends to wetlands with a continuous surface connection to relatively permanent bodies of water, such that they are indistinguishable from those waters.

The practical consequence of Sackett: many wetlands are outside federal jurisdiction, which shifts the question to state wetland and water quality law — which in some states is as protective as the federal program and in others is nearly absent. Check the state program; the federal answer is no longer the whole answer.

Other overlays: state water quality certification of federally licensed projects; endangered species requirements, which have reshaped operations on several major systems; dam licensing; and the public trust doctrine, under which states hold navigable waters in trust for the public — a doctrine that in some states constrains the exercise of otherwise valid water rights.

Part IX: Five disputes

The junior who wakes up curtailed

A rancher with a 1961 priority receives a curtailment order in July: stop diverting, the 1889 right downstream has called.

There is no answer based on need, investment, or fairness. Priority is the system, and the senior takes in full before the junior takes anything.

What can actually be argued:

Futile call. If the water curtailed would not physically reach the senior in usable quantity because of channel losses, the call may be futile and unenforceable. This requires hydrology, not assertion.
The senior is not using it beneficially, or is calling for more than the right's historical consumptive use.
The senior's right has been partially forfeited through extended non-use.
Administrative error in the priority ordering or the accounting.

What can be done instead of arguing:

Buy or lease the senior right, permanently or for the season. Short-term forbearance agreements are common and frequently cheaper than litigation.
Provide augmentation — replacement water delivered to the senior, or to the stream, offsetting the depletion.
Join or form a water bank or augmentation plan, which many basins operate.

And the lesson for anyone acquiring land: the priority date is the most important fact about a water right, more important than the quantity on the paper. An 1889 right for a modest quantity is worth more than a 1972 right for a large one.

The buyer who bought the land and not the water

A purchaser closes on an irrigated farm and discovers the water right was severed and sold three years earlier.

This is entirely avoidable and it happens constantly. In some states water rights are appurtenant and pass with the land unless expressly reserved; in others they are separate property conveyed by separate instrument.

Diligence that would have prevented it:

Obtain the right's paper — permit, certificate, or decree — with the priority date, source, quantity, point of diversion, place and purpose of use, and season.
Search the state water agency's records in the seller's name and against the parcel, not just the county recorder.
Confirm no pending transfer or change application.
Confirm no forfeiture proceeding, and obtain evidence of recent use.
Include an express conveyance of the water right in the deed and in a separate assignment if the state requires one.
Address it in the purchase agreement as a condition, with a representation and a title contingency.

And check title insurance. Standard policies frequently except water rights. If the water is the value of the property, that exception matters more than anything else in the policy. See Buying or Selling a Home.

The city buying agricultural water

A municipality acquires irrigation rights and applies to change the use to municipal and the point of diversion downstream.

The change application is the whole proceeding, and it will be protested.

What the applicant must prove:

Historical consumptive use — not the paper right, but the water actually consumed by the crop over a representative period, established by diversion records, crop and acreage history, climate data, and consumptive use modeling. This is the technical heart of every transfer.
No injury to other appropriators, considering the change in timing, location, and return flows. Converting a partially consumptive irrigation use to a fully consumptive use removes return flow that juniors relied on.
Compliance with any basin-specific rules on the transfer of agricultural water.

What protestants argue: inflated historical use; injury from lost return flows; changed timing; and — where the state recognizes them — public interest and area-of-origin considerations protecting the community losing the water.

How these resolve: usually by negotiated conditions — a reduced transferable quantity, delivery of replacement water in specified months, retained fallowing obligations, dry-year leasing rather than permanent transfer, or payments to the area of origin.

The well that dried up the creek

Junior groundwater pumpers in a valley are ordered to curtail because their pumping depletes a stream serving senior surface rights.

This is conjunctive management, and it is the most contentious subject in western water law, because the pumpers have often operated for decades under permits the state issued.

The technical problem is delay. Pumping today may deplete the stream in five, twenty, or fifty years, and the modeling that connects a particular well to a particular reach is genuinely difficult and genuinely contestable.

What pumpers can do:

Challenge the model — the aquifer parameters, the depletion timing, the assignment of responsibility among wells.
Form or join a mitigation or augmentation plan, delivering replacement water to the stream. This is the dominant practical solution.
Acquire senior surface rights and dedicate them instream.
Negotiate a phased reduction rather than immediate curtailment.

What everyone should understand: an aquifer being mined is a physical fact, and no legal doctrine creates water. The disputes are about who absorbs a reduction that is coming regardless.

The tribe with an unquantified right

A stream is fully appropriated among ranchers and a town. The tribe's reserved right, with an 1868 priority, has never been quantified.

Every junior right on the stream is contingent on an amount nobody has determined — and under Winters the right is senior, is measured by the purposes of the reservation rather than by past use, and cannot be lost by non-use.

Why litigation is rarely the answer for anyone. A general stream adjudication quantifying the right takes decades. The tribe may win a large paper right with no infrastructure to divert it. The juniors face ruin on paper without knowing when. Nobody gets water from a decree.

Why settlements dominate. A negotiated Indian water rights settlement typically produces: a quantified tribal right, often below the maximum legal claim; federal funding for delivery infrastructure, which converts a paper right into wet water; protection for existing junior uses, sometimes through subordination or shortage-sharing; authority for the tribe to lease or market some portion; and congressional ratification with a waiver of further claims.

For a practitioner representing anyone on such a stream, the advice is the same: participate in the settlement process early, understand that the tribe's position is legally strong, and negotiate for certainty rather than for victory.

Part X: Water rights as property, and what that means

Appropriative water rights are property, and treating them like property clarifies a great deal.

They can be bought, sold, leased, mortgaged, inherited, and taxed — subject to the transfer rules above. A market exists, and prices in over-appropriated basins can be extraordinary.

They can be encumbered. Lenders take security interests in water rights, and a lender financing irrigated agriculture will insist on it. The perfection mechanics differ by state — sometimes recorded with the county, sometimes with the water agency, sometimes both. Getting this wrong leaves a lender unsecured on the most valuable asset.

They are a distinct title question. Water rights are frequently excepted from standard title insurance policies, and a separate water rights opinion or a specialized endorsement may be required. In an irrigated-land transaction, the water title work is more important than the land title work.

They can be lost by inattention. Forfeiture for non-use, failure to file required reports, failure to respond to an adjudication notice, and failure to maintain a diversion structure all extinguish or impair rights that were perfectly valid.

They are subject to regulation. A vested right does not exempt the holder from measurement requirements, reporting, fish passage obligations, water quality rules, or the terms of a decree. Regulation of the exercise of a right is not a taking of the right, though the line is litigated.

And they can be conditioned by contract. Most delivered water in the West arrives through an irrigation district, a ditch company, a canal company, or a federal reclamation project — and the user's relationship is with that entity, governed by its bylaws, shares, assessments, and delivery rules, not directly by the state right. Read the district's rules; they may matter more than the underlying right.

Part XI: Instream flow and the environmental turn

For most of the doctrine's history, leaving water in a stream was not a beneficial use, which meant environmental protection had no place in the priority system.

That has changed substantially, through four mechanisms:

Instream flow appropriations. Most western states now recognize instream flow as a beneficial use, though typically only the state or a designated agency may hold such a right — which limits its usefulness because those rights are junior to everything senior to them.

Transfers to instream use. A private party may acquire a senior right and dedicate it to instream flow, carrying its original priority. This is the most powerful tool available, because it brings seniority into the environmental column, and water trusts have used it extensively.

Minimum flow conditions attached to new permits and to reservoir and hydropower operations.

Federal endangered species requirements, which have reshaped operations on several major systems and which operate independently of state water law — a source of enduring friction, because a federal requirement can override a state-decreed priority.

And the public trust doctrine, under which states hold navigable waters in trust for the public. In some states this has been held to constrain the exercise of otherwise valid water rights where a diversion harms trust resources, and to impose a continuing supervisory duty on the state. Its reach varies enormously by state, and it is a doctrine worth checking in any dispute involving a lake, a navigable stream, or a fishery.

The practical point for anyone holding or acquiring rights: environmental constraints are now a permanent feature of water administration, they attach to permits and to operations rather than to the underlying right, and they are more likely to increase than to relax.

Part XII: Practical advice

If you own or are buying a water right:

Get the paper. The permit, certificate, or decree, with the priority date, quantity, source, point of diversion, place and purpose of use, and season.
Verify it exists in the state's records, and confirm it has not been forfeited.
Document use every year. Photographs, meter readings, crop records, delivery receipts. In a forfeiture proceeding, the burden practically falls on the user to show use.
Do not assume the deed conveys it. Water rights may be appurtenant and pass with the land, or may be severable and separately conveyed. Read the conveyance and check the state's rule.
Watch for adjudication notices and respond.

If you want to make a new use:

Find out whether the source is over-appropriated. In many basins, new appropriations are unavailable and the only route is acquiring an existing right.
Consider acquisition and transfer instead, and budget for the historical consumptive use analysis and the no-injury protest process.
Check groundwater management area rules, permit moratoria, and any augmentation requirement.
Check the federal and state permitting overlay for any physical work in or near a waterway.

If you are in a dispute:

Establish the priorities of every affected right first.
Get the hydrology. Water disputes are engineering disputes with a legal frame.
Consider the administrative route — most states have a water agency with authority to regulate, curtail, and resolve.
Consider settlement. Water disputes litigated to judgment take years and produce decrees neither side fully controls.

Part XIII: Water in the East, where the rules are changing

Eastern water law was long treated as a backwater — abundant supply, few disputes, a common law of reasonableness that rarely had to do any work. That is no longer accurate, and the direction of travel is clear.

The pressures. Municipal growth in the Southeast, agricultural irrigation expanding into humid regions, thermoelectric cooling, data centers with substantial water demand, drought sequences that are longer and more frequent, and interstate disputes on rivers that were never thought to need allocation.

The legal response has been the regulated riparian model, and most eastern states have now adopted some version: a permit for withdrawals above a threshold, issued for a term, with conditions, metering and reporting, and authority to curtail during drought under a declared drought plan.

What that means practically for an eastern water user:

The common law is background; the permit is the right. Reasonable use still governs disputes between neighbors, but the operative question for any substantial withdrawal is the permit's terms.
Permits have terms and must be renewed, which introduces a renewal risk that riparian doctrine never had.
Drought plans matter more than priority, because eastern systems generally curtail by category — often protecting domestic and public supply first — rather than by seniority.
Registration matters. Several states grandfathered existing uses only if registered by a deadline. A use that was never registered may be worth nothing.
Interbasin transfers are the flashpoint. Moving water out of the basin of origin draws the strongest opposition and the most restrictive rules.

And the interstate dimension has arrived. Equitable apportionment actions and compact disputes over eastern rivers have proceeded in the Supreme Court's original jurisdiction, applying the same framework used on western streams — Kansas v. Colorado supplies the doctrine regardless of geography.

The practical advice for an eastern user: find out whether your withdrawal requires a permit; register any grandfathered use; read the state's drought plan and know which curtailment category you are in; meter and report accurately; and, if you are planning a facility with substantial water demand, treat water supply as a permitting question at the site selection stage rather than at the construction stage.

Part XIV: Surviving a general stream adjudication

A general stream adjudication is the largest and least understood proceeding most water right holders will ever be part of, and the failure mode is passivity.

What it is. A comprehensive judicial determination of every right on a stream system — surface and, in many, groundwater — establishing for each: the claimant, the source, the priority date, the quantity, the point of diversion, the place and purpose of use, and the season. The product is a decree that becomes the definitive record, administered thereafter by a watermaster or state agency.

Why it happens. Because nobody knows who owns what. Rights accumulated over a century through permits, decrees, common law claims, and use without paper, and administration is impossible without a single authoritative list. A federal statute permitting joinder of the United States, together with Colorado River deference, allows federal and tribal claims to be resolved in the same proceeding.

The sequence:

Commencement and notice to all claimants — the piece of mail that must not be ignored.
Statements of claim, filed by each claimant on the court's form, by a deadline.
Field investigation by the state agency, which visits and maps diversions and irrigated acreage.
A preliminary or draft report proposing findings for each right.
Objections, on a short deadline, by anyone disputing any right — theirs or a neighbor's.
Hearings, often before a special master.
Interlocutory and final decrees.
Administration under the decree, indefinitely.

What a claimant must do:

File the statement of claim by the deadline. A right not claimed may be extinguished. This is the single most important act.
Claim accurately. Overstating invites objection and can undermine credibility on everything else; understating locks in a smaller right forever.
Assemble the evidence now: the permit or decree; historical diversion records; aerial photographs by year showing irrigated acreage; crop records; ditch company or district records; tax records; affidavits from people who remember the use; and any prior decree.
Read the draft report line by line and object to errors in your right — the priority date, the quantity, the acreage, the season, the point of diversion.
Read your neighbors' entries too. An inflated right upstream will curtail you for the rest of the decree's life.
Consider a coalition. Ditch companies, districts, and similarly situated claimants routinely share technical experts and counsel, which is the only affordable way for a small claimant to participate meaningfully.

Expect it to take decades, and expect the decree to outlive you. That is precisely why the statement of claim deadline matters so much: the cost of ten hours' work now is the difference between a right that exists and one that does not.

Part XV: The shortage problem, stated plainly

Nearly every stress in this field traces to one arithmetic fact: on many systems, the rights on paper exceed the water in the river, and the gap is widening.

How it happened. Compacts and decrees allocating major rivers were negotiated using hydrology from unusually wet decades. Appropriations continued after the reliable supply was fully committed. Groundwater was permitted as though it were a separate resource, when much of it is stream water arriving on a delay. And demand grew — municipal, agricultural, industrial, and, more recently, from facilities with large cooling loads.

What the legal system does with a shortage. Prior appropriation has an answer, and it is brutal and clear: juniors go to zero so seniors stay whole. Riparian systems have the opposite answer: everyone reduces together, moderated by permit conditions and drought plans. Neither answer creates water, and both produce enormous pressure to negotiate around the doctrine rather than apply it.

The mechanisms that have actually emerged, and that a practitioner will encounter constantly:

Shortage-sharing agreements among states and among users, allocating reductions by formula rather than by strict priority.
Voluntary fallowing and dry-year leasing, in which irrigators are paid not to divert in dry years — the least disruptive real reallocation available.
Water banks that hold and allocate rights or credits.
Augmentation and mitigation plans that let junior pumpers continue by replacing depletions.
Conservation programs paired with statutory protection so that saved water is not forfeited under "use it or lose it."
Municipal acquisition of agricultural rights, with conditions protecting the area of origin.
Reuse and recycling, which raises its own legal question: reused water is water that does not return to the stream, which affects downstream rights.

The honest assessment. Water law is a nineteenth-century allocation system operating on a twenty-first-century hydrology. It is not going to be replaced — the property interests are too settled and the political economy too entrenched — so it will be adapted at the edges, through markets, settlements, and negotiated shortage-sharing. For a lawyer, that means the valuable skills in this field are increasingly transactional and negotiated rather than adversarial, and the valuable knowledge is hydrologic as much as doctrinal.

And a note for landowners. Water is frequently the most valuable asset attached to rural land and the one least examined at purchase. The priority date, the quantity, the evidence of continued use, and whether the right actually conveys are the four facts that determine the value of the property — more than acreage, soil, or improvements. Get them before closing.

Part XVI: The vocabulary

Water law runs on terms that mean something precise and that outsiders use loosely.

Acre-foot — the volume covering one acre one foot deep, roughly 325,851 gallons. The standard unit of water in the West.

Cubic feet per second (cfs) — a rate of flow, not a volume. A right expressed in cfs limits the instantaneous rate; a right in acre-feet limits the annual total. Many rights have both, and confusing them is a common error.

Diversion vs. consumptive use — what is taken from the stream versus what is actually consumed and does not return. Only consumptive use is transferable.

Return flow — water that runs off or percolates back to the stream after use, and on which downstream rights depend. The reason a transfer can injure juniors even at an unchanged diversion.

Priority date — the date the appropriation began, determining rank. The single most important fact about a western water right.

Call — a senior's demand that juniors cease so the senior can be satisfied. Futile call — a call that would not deliver usable water to the senior, and so is not enforced.

Beneficial use — both the measure and the limit of an appropriative right.

Appurtenant — attached to specific land and passing with it, as opposed to a severable right conveyed separately.

Duty of water — the quantity per acre allowed for irrigation in a given area, often set by decree or rule.

Historical consumptive use — the quantity actually consumed over a representative period; the transferable amount.

Augmentation / replacement supply — water delivered to offset a depletion, allowing an out-of-priority diversion to continue.

Conjunctive management — administering groundwater and surface water as one connected resource.

Safe yield / sustainable yield — the withdrawal an aquifer can sustain; exceeding it is mining.

Adjudication — the comprehensive judicial determination of all rights on a system; the resulting decree is administered by a watermaster.

Reserved right — a federal or tribal right implied by the reservation of land, with the reservation's date as its priority, not lost by non-use.

Practicably irrigable acreage — a quantification standard for agricultural reservations approved in Arizona v. California.

Equitable apportionment — the federal common law division of an interstate stream, from Kansas v. Colorado.

Waters of the United States — the Clean Water Act's jurisdictional term, narrowed in Sackett v. EPA to require a continuous surface connection for adjacent wetlands.

Frequently asked questions

Do I own the water under my land? Depends on the state and the doctrine. In most western states groundwater is appropriated and permitted; in some eastern states pumping is governed by reasonable use; nowhere is the answer simply "yes."

What is a "call"? A senior appropriator's demand that juniors cease diverting so the senior right can be satisfied.

Can I sell my water right? Generally yes in appropriation states — but only to the extent of historical consumptive use, and only without injury to other appropriators.

Will conserving water cost me my right? Historically it could, under "use it or lose it." Many states now protect conserved water; check yours before fallowing or improving efficiency.

What are Indian reserved water rights worth? Often a great deal, because the priority date is the date of the reservation and the right is not lost by non-use. Most are resolved by negotiated settlement.

Does the Clean Water Act still cover my wetland? Only if it has a continuous surface connection to a relatively permanent water after Sackett. Check state law, which may still regulate it.