Durham residents received a notice in their most recent water bill recommending that if you wash your car at home, do so over gravel or grass. The water will seep into the ground rather than run off into the storm drain, which, in turn, sends it directly into rivers and streams. And remember, the water contains not only soap, but also can carry residues of paint, wax, gasoline and exhaust fumes—all pollutants that can harm the environment.
If you must wash your car at home, don't waste water by leaving the hose running. Don't use paper towels, but washable cloths or sponges. Instead of using harsh chemicals—not good for your hands or lungs—concoct your own biodegradable car wash: Mixing one cup of liquid dishwashing detergent and three-quarters of a cup of powdered laundry detergent with three gallons of water. Make sure the detergents are chlorine- and phosphate-free and non-petroleum-based. Seventh Generation, Biokleen and Ecover all have good enviro credentials. However, note that soap can damage some car finishes and strip the wax, although GNLD's LDC cleanser (which was used on penguins covered in oil after a spill near Africa) has received good marks for its friendliness to the environment and car finish.
While commercial car washes admittedly consume green space with swaths of concrete, they also are legally required to drain their wastewater into sewer systems, so it is treated before being discharged into waterways. Patronize car washes that recycle and/or reuse their water. Some car washes use half as much water per car—45 gallons—than you would at home—80 to 140 gallons.