While we were blathering on mindlessly in a comment thread about the water exported form California via alfalfa exports, Peter Gleick helpfully jumped in with come actual data:

California’s total water footprint is an estimated 64 million acre-feet of water. That’s more than double the amount of water that flows down both of the state’s two largest rivers, the Sacramento and San Joaquin, in an average year. An estimated 38 million acre-feet of water is used to produce goods and services within California. Half of that water is used for goods that are then exported and consumed outside the state. The remainder – about 19 million acre-feet of water – is used to produce goods that are consumed in California. An additional 44 million acre-feet of water is required to produce the goods and services that are imported into California and consumed here, making California a net importer of virtual water.

“As pressures on water resources intensify, evaluating our impact on the world’s water resources becomes increasingly important; the water footprint is one way to quantify this impact,” said Julian Fulton, lead author of the report. “Most of California’s water footprint is external, meaning that Californians are more dependent on water resources from other places than in-state.”