Concept
In the American legal system, prior appropriation water rights is the doctrine that the first person to take a quantity of water from a water source for "beneficial use" (agricultural, industrial or household) has the right to continue to use that quantity of water for that purpose. Subsequent users can take the remaining water for their own use if they do not impinge on the rights of previous users. The doctrine is sometimes summarized, "first in time, first in right". Prior appropriation rights do not constitute a full ownership right in the water, merely the right to withdraw it, and can be abrogated if not used for an extended period of time. Water is very scarce in the West and so must be allocated sparingly, based on the productivity of its use. The prior appropriation doctrine developed in the Western United States from Spanish (and later Mexican) civil law and differs from the riparian water rights that apply in the rest of the United States. The appropriation doctrine originated in Gold-Rush–era California, when miners sought to acquire water for mining operations. In the 1855 case of Irwin v. Phillips, Matthew Irwin diverted a stream for his mining operation. Shortly afterward, Robert Phillips started a mining operation downstream and eventually tried to divert the water back to its original streambed. The case was taken to the California Supreme Court, which ruled for Irwin. The legal details of prior appropriation vary from state to state. Under the prior appropriation system, the right is initially allotted to those who are "first in time of use"; these rights of withdrawal can then trade on the open market, like other property. For water sources with many users, a government or quasi-government agency is usually charged with overseeing allocations. Allocations involving water sources that cross state borders or international borders can be quite contentious, and are generally governed by federal court rulings, interstate agreements and international treaties.