talking about groundwater, we're really talking about water below the water table. >> stahl: jay famigliettiarth sciences professor at the university of california irvine, is a leading expert on groundwater. >> famiglietti: it's like a sponge. it's like an underground sponge. >> stahl: he's talking about the aquifers where groundwater is stored-- layers of soil and rock, as he showed us in this simple graphic, that are saturated with water and can be drilled into, like the three wells shown here. you can actually pump it out of the crevices? >> famiglietti: imagine like trying to put a straw into a sponge. you can actually suck water right out of a sponge. it's a very similar process. >> stahl: sucking the water out of those aquifers is big business these days in the central valley. well driller steve arthur is a very busy man. >> steve arthur: all the farmers, they don't have no surface water. they've got to keep these crops alive. the only way to do that is to drill wells, pump the water from the ground. >> stahl: so it's either drill or go out of business? >> arthur: yes. >> stahl: so the