Why is washing at home so bad for the environment?

WASTES WATER. Engineering studies have shown that a 5/8" hose running at 50psi uses 14 gallons of water per minute. As many as 140 gallons of water could be used in a ten minute home carwash, most of it wasted.

POLLUTES STORM DRAINS. Washing at home sends all the corrosive and toxic substances that are on your vehicle and on the street, including asphalt, engine and brake residue, antifreeze, grease, oil, rust and asbestos into the storm drain system. Storm drains are designed to handle rainwater and thus the water is not subject to any pretreatment before being released into our areas rivers and streams.

CLOGS STORM DRAINS. As previously mentioned, storm drains were designed to handle rainwater. When car washing is done at home the dirt and grime is carried into the storm drains which can clog them from working most efficiently during our rainy season.

HARMS WILDLIFE. Even if bio-friendly soap (or no soap at all) is used, hosing off a car's body and wheels dislodges pollutants that can end up in rivers, lakes, and streams. In a 2006 study it was shown that these chemicals when released into our areas rivers and streams can damage fish's mucus membranes and gills and wash away natural oils that help them absorb oxygen and ultimately lead to the loss of the fish.

Source:  Stormwater: The Journal for Surface Water Quality Professionals