water rights, in law, the qualified privilege of a landowner to use the water adjacent to or flowing through his property. The privilege, also known as riparian rights, may be modified or even denied because of the competing needs of other private-property holders or of the community at large. There is no private ownership of such water in most cases, and hence it cannot ordinarily be impounded and sold. The owner, however, may use the water for his ordinary private purposes, such as stock watering or irrigation, and then return the unused residue. Most uses of water affect its purity to some degree, and recent environmental legislation has greatly restricted the amount of permissible water-use pollution. Water projects such as dams that threaten the survival of rare species can be blocked under the Endangered Species Act. In certain parts of the United States—especially in the arid and semiarid regions of the Southwest—the prior appropriation rule applies, and the first user of water, whether or not he owns land abutting the water, has the unrestrained right to it without regard to his neighbor's needs. Throughout the United States, the rights of private owners in water can be set aside to construct public works, such as dams and irrigation projects, and agreements at the local, state, and regional level may govern water rights and use. The ownership of a stream bed may depend upon whether the stream is or is not a navigable water. If it is navigable, some states claim title to the bed, whereas in other states the rule is the same as in the case of nonnavigable streams, namely that an abutting owner's property extends to the middle of the bed and that those with property along both banks of a stretch own the enclosed portion of the bed. If the stream is navigable, the owner must permit public use for passage and transportation; if it is nonnavigable, the owner may exclude all but other riparian owners from using the stream. If the stream shifts course, ownership of the former bed is not affected. Underground and percolating waters have no easily determined course, and the usual American practice is not to restrict a landowner who taps and exploits these waters; however, in some states the rights of those who may be adversely affected must be considered.
See S. Bhatt, Environmental Laws and Water Resources Management (1986).