SAN FRANCISCO — Call them the fortunate ones: Nearly 4,000 California companies, farms and others are allowed to use free water with little oversight when the state is so bone dry that deliveries to nearly everyone else have been severely slashed.

Their special status dates back to claims made more than a century ago when water was plentiful. But in the third year of a drought that has ravaged California, these “senior rights holders” dominated by corporations and agricultural concerns are not obliged to conserve water.