The best place to wash your car is a commercial car wash. Commercial car washes collect and treat the dirty, soapy water so that it does not go directly into a pond, stream or river. If you must wash your car at home, do so over a lawn or gravel area to be sure the soap and dirt don't flow into a storm sewer. Use biodegradable soaps to wash your vehicle, using as little water as possible. Shut off water while washing your car, or use a trigger nozzle to stop the flow. Remember not to leave your car on the lawn when you have finished washing it.