By Janet Raloff
In the arid West, water has always been scarce. To limit wars over this lifeblood, states during the 19th-century mining era began issuing to some of their landowners legal entitlements to a share of the water flowing through rivers and lakes. Called water rights, these formal entitlements now pass down, with the land, from owner to owner as a form of property.
The entitlements establish that when water supplies begin drying up, landowners holding the oldest claims are to get their full allotment of water before any is dispensed to holders of more recently established water rights. Legally, therefore, those who inherit or purchase land carrying the oldest water rights stand at the head of the line to the public water trough.