The two main environmental issues concerning car washing are water consumption and water pollution. Commercial car washes are designed to minimize both. Of the alternatives to the commercial car wash, washing your car in the driveway may be one of the most eco-hostile household chores on your to-do list.

Most commercial car washes use low-flow, high-pressure nozzles and computerized controls, which reduce their water consumption to 45 gallons per vehicle or less. Systems equipped to recycle and reuse rinse water can use as little as eight gallons per vehicle. To avoid contaminating sensitive ecosystems with large volumes of car wash run-off, government regulations require commercial car washes to treat wastewater either on-site or through a treatment plant. Treatment involves the filtering, removal, and biological and chemical breakdown of harmful contents so that the water can be released relatively harmlessly back into the environment.

The process of washing your car at home with an open hose can consume more than 100 gallons of water. Less water is used if the hose is turned off between rounds of rinsing (either by hand or with an automatic shut-off nozzle). Unlike the wastewater produced within your home, the run-off from a driveway car wash does not enter the public sewer system and, thus, does not undergo treatment.

Typically, the soapy water generated by a home car wash follows the forces of gravity into the gutter. As it is channeled along, the water picks up additional the dirt, debris, chemicals, and other pollutants in its path. This toxic concoction then pours into a storm drain, and often eventually enters a stream, lake, river, or wetland where it can damage the health of plants, fish, birds, and other wildlife. Highly polluted run-off can also damage the suitability of water bodies for swimming, fishing, and providing drinking water.

Further, just because a particular product claims to be biodegradable, doesn’t mean it’s good for the environment. Any chemical that breaks down over time is biodegradable, regardless of its effect on living organisms. In some circumstances, the byproducts of biodegradation are more toxic than the original compound.

Although the commercial car wash is the best option (especially if you combine it with other errands while you’re out), if you must do a home wash it’s recommended that you park your vehicle over grass or gravel so that the soap, oil, and dirt in the wastewater can be filtered by the soil. You can minimize the environmental impact of this toxic brew by using an eco-friendly soap (free of phosphates, chlorine, and petroleum derivatives), and conserve water by using a flow-control hose nozzle.

One last word: If you’re involved with fundraising for a school, athletic, or charitable organization, for all the reasons above, resist the urge to promote a parking lot car wash.