SAN FRANCISCO, Calif. -

Throughout California's desperately dry interior, those with water to spare are cashing in.

As a third dry summer forces farmers to fallow fields and lay off workers, three water districts in the state's agricultural heartland are making millions of dollars by auctioning off their private, underground caches.

Records show nearly 40 others also are seeking to sell their surplus water this year.

Economists say it's been decades since the water market has been this hot. In the last five years alone, the price has grown tenfold, shooting to as much as $2,200 an acre-foot - enough to cover a football field with a foot of water.

But some water economists say California needs to do more to regulate the water market to keep aquifers from being depleted from short-term sales.