The scarcity of water in the Rocky Mountain and southwestern states has led to the development of a system of water allocation very different from that which exists in regions graced with more abundant rainfall. Rights to water are established by actual use of the water, and maintained by continued use and need. Water rights are treated similarly to rights to real property, can be conveyed, mortgaged, and encumbered in the same manner, all independently of the land on which the water originates, or on which it is used. The following is a summary of the legal framework governing water rights in the arid areas of the country.

Doctrine of Prior Appropriation

The use of water in many of the states in the western U.S. is governed by the doctrine of prior appropriation, also known as the "Colorado Doctrine" of water law. The essence of the doctrine of prior appropriation is that, while no one may own the water in a stream, all persons, corporations, and municipalities have the right to use the water for beneficial purposes. The allocation of water rests upon the fundamental maxim "first in time, first in right." The first person to use water (called a "senior appropriator") acquires the right (called a "priority") to its future use as against later users (called "junior appropriators"). In order to assure protection of senior water right priorities and to maximize the use of this scarce and valuable resource, many states have adopted detailed schemes for the determination and administration of water rights. These state regimens define to a large extent just what a water right is.

Acquisition of Water Rights

To create a water right, one must make an appropriation. The essential elements of an appropriation are the diversion of water and its application to a beneficial use. A diversion is made simply by removing water from its natural course or location, or by controlling water that remains in its natural course. The requirement of application to beneficial use is satisfied by irrigation, mining and industrial application, stock watering, domestic and municipal use, and other non-wasteful economic activities.

The definition of beneficial use of water has expanded in recent years to include environmental dust control and snowmaking, among others. An appropriator may remove the water from its source and put it to beneficial use at any location. In contrast to riparian water rights, there is no geographical limitation as to place of use. Concomitantly, the ownership of land bordering a watercourse carries with it no right to the use of the water in the absence of an appropriation. To gain access to the water source and to transport it to the place of use, the appropriator must obtain an easement, either by contract or grant, or by prescription (continuous, adverse use of an existing ditch). Many state laws provide the appropriator with a private right of condemnation to secure an easement between the source of the water and the place of use.

Some western states recognize both absolute and conditional water rights. Where an appropriation has been completed by diversion and beneficial use of the water by the time the water right is adjudicated or a permit is issued, the water right is described as absolute, or completed. An appropriator may, however, obtain a conditional water right before the water has actually been used. This is useful primarily where large water projects are involved, the construction of which will take some time to complete. The appropriator may obtain a decree or permit to protect his priority before completing the appropriation in order to assure that water which was available in priority at the time the project was initiated will still be available after its completion. When a firm intent to appropriate certain water is established and certain acts in furtherance of the project are undertaken, a conditional water right may be recognized, with a priority date as of the date the first step in the project was initiated. If the project proceeds with reasonable diligence, an absolute water right can be obtained upon completion of the project, with a priority date which "relates back" to the date of the conditional right, that is, the date the project was launched.

Because the water right system is founded upon beneficial use of the resource, a lack of use can result in an "abandonment' or "forfeiture" of the right. Most western state laws provide for the loss of a water right if the water is not diverted and used for more than a specified period of time, sometimes as little as five years. Some states also require proof of an "intent to abandon" the water right. Such intent may be presumed if the non-use has occurred for an unreasonably lengthy period.

Types of Water Rights

Water rights are of two general types, direct flow and storage. A direct flow right is generally measured in terms of a rate of flow, not a total volume of water. For example, a direct flow right for "1.0  c.f.s." means that the appropriator is entitled to divert water from a stream or a well at a rate of not more than one cubic foot of water per second of time. He may continue to take water at this rate of flow for so long as it is physically available in priority and he needs the water for beneficial use. If a water right was initiated to irrigate a 40 acre tract, the need, or "duty" of that water right is measured as the amount of water necessary to irrigate properly that 40 acre tract.

The duty of water concept operates as a limit on the amount of water that may be diverted under a priority and is designed to prevent waste. In the example, the appropriator may divert 1.0 c.f.s. to the 40 acre tract only until it is fully irrigated. One c.f.s. of water flow is equivalent to 449 gallons per minute.

A storage water right is measured in terms of volume. For instance, the owner of a reservoir may have the right to store up to 1,000 acre feet of water each year, to be used at some later time for a beneficial use. An acre foot is that amount of water required to cover an acre of ground with one foot of water (43,560 cubic feet or 325,851 gallons). Sometimes a limit is placed on the rate at which water can be stored, such as a right which allows for storage of 1,000 acre feet, to be stored at a rate no greater than 5.0 c.f.s. Storage rights are usually only for one filling of the storage vessel per year.

Ground Water

Rights to water from underground vary in their treatment in the different western states. Some states treat tributary ground water--water that is hydrologically connected to surface flow - in the same manner as described above for surface water rights. Such ground water is integrated into the surface water rights priority system. Thus, a well withdrawing tributary ground water is treated in precisely the same manner as a surface diversion from a stream for the purposes of administration of water rights in accordance with the priority system. There may be a legal presumption that all ground water is tributary.

Some states recognize a completely different type of water right in nontributary ground water, that is water coming from an underground aquifer which, because of its unique geology and/or depth below the ground surface, contains water that has no connection to any natural surface stream. Because there is no impact from the withdrawal of this water on the surface stream system, these water rights are not integrated into the water right priority system. Thus, water can be withdrawn from nontributary wells regardless of whether senior surface water rights are receiving their full entitlement. In at least one of the western states, ownership of nontributary ground water is tied to the ownership of the land overlying the water itself.

Many western states also have legislative schemes that allow for the designation of critical ground water areas. These are usually areas in which ground water withdrawals have been a primary source of water supply for municipal or agricultural water uses, and in which aquifer water levels are dropping. The purpose of the designation is to allow special rules to be established for protection of the aquifer resource, yet permitting some continued development, or mining, of the underground water. Priority systems may be put into place, or modified to require all water users to share the burdens pro rata. New wells may be permitted only if the proposed appropriation will not unreasonably impair existing rights from the same source.

Administration of Water Rights

A state agency or official is charged with the administration of all water rights within the state, usually an executive branch department of water resources or the state engineer. Additionally, there may be a "water commissioner" to administer the allocation of water on a particular stream or streams. Competition for water, as well as proper enforcement of the priority system, requires comprehensive administration. For instance, those persons with the oldest priority dates (senior water rights) can require that others stop taking water so that the water remaining in the stream system will reach the diversion works of the senior users. This type of demand by senior water rights is known as a "call." In times of shortage when senior water rights are calling for water, water users may be shut off in inverse order of priority by order of state administrators. The predicted administration of a water right must be considered in the evaluation of the yield that can be expected from that water right, or its value.

Replacement Plans

The laws of several of the western states provide for replacement plans which are schemes to balance new uses of water with the dedication of other existing water rights to the stream, so that the stream, as a whole, suffers no net decrease. A replacement plan is most often used to allow the out-of-priority diversion of water from the tributary stream system and the replacement of the depletion caused by that diversion from some other source. Sources of replacement water include senior direct flow water rights no longer used for their original purpose, nontributary ground water, or water stored in a reservoir and available for later release. Approval of a replacement plan will permit the water user to continue diversions of water when curtailment would otherwise be required to meet a valid senior call for water.