Prior-appropriation water rights

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.

Source: Wikipedia — Prior-appropriation water rights (CC BY-SA 4.0)