air. reporter: just this week, a water supplier to 6 million southern californians declared an emergency, severely limiting nonessential water use. the drought impacting parched farmlands and american dinner tables. the tomatoes, the sweet corn, melons, things that we would normally have at the stores aren t going to be grown in the quantity this year than we re used to reporter: california provides two-thirds of the u.s. supply of fruits and nuts we re blessed with this mediterranean-type climate here in california that nobody else has and we can grow crops here that can t grow anywhere else. reporter: farmer bill dietrich grows tomatoes but not now. no tomatoes this year because this water has got to be put to use on other crops that, for us, is less risky. reporter: many farms partly rely on groundwater, but if it s not stored in the good years, it can leave fields like this high and dry in the