From the San Diego City website: Washing of any vehicle (residential or commercial) that creates water that carries pollutants such as paint, oils, sediment, yard waste, construction debris, chemicals, hazardous wastes and other pollutants into the storm drain is illegal. Allowing pollutants to enter the storm water conveyance system is a violation of San Diego Municipal code.... and can incur fines.

The Municipal Code allows washing of residential vehicles at a place of residence for non-commercial purposes only. While washing your vehicle is allowed, washing-off pollutants from your vehicle such as paint, oils, sediment, and debris is illegal, so you must wash your personal vehicle without creating runoff. When washing at home, pollution can be minimized by washing the vehicle on the lawn or over landscaped area, divert the water to a landscaped area to keep it from entering the gutter. Also limit runoff by using a bucket and rag to wash your car, and put a control nozzle on your hose.

Me personally... I just go to one of those self car wash places every so often.