The sewers in southern California drain into the ocean. As a result one of the biggest ocean pollutants of coastal water is urban run off. The infrequent rains, car washing, etc sweep up pollutants like fertilizers, bug sprays, animal feces, and carries it right in the oceans.
This is an article on green driveways. Having a grass driveway that is drought tolerant would be a step in the direction of cleaning up a small part of the run off.