Under the riparian principle, all landowners whose property is adjacent to a body of water have the right to make reasonable use of it. If there is not enough water to satisfy all users, allotments are generally fixed in proportion to frontage on the water source. These rights cannot be sold or transferred other than with the adjoining land, and water cannot be transferred out of the watershed.

In the western United States, water rights are generally allocated under the principal of prior appropriation, which treats water as a resource unrelated to land.

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