We've already touched on car washes' superior water reclamation systems, features that make car washes a much more water efficient option for responsible vehicle cleaning vs. driveway washing (particularly in drought areas). But there's another great reason for you to turn to your local car wash instead of the hose and bucket: water runoff.
When a vehicle owner washes their car in their driveway they usually rely on commercial car wash detergents and soaps rich in surfactants and other cleaning compounds, including high levels of sodium or disoduim phosphate. Once the car has been scrubbed down all the suds (along with brake dust, automotive oils, and heavy metals) are then rinsed off and flow towards the nearest storm sewer, which likely then flows towards the nearest body of water.
But rather than harming organisms directly these phosphates actually act as a powerful nutrient and stimulate vastly increased algae growth, resulting in huge algae 'blooms' that block out sunlight for the plants below and rapidly deplete oxygen from the water - oxygen that local fish and aquatic wildlife need to survive. Huge die-offs have been reported, and the algae itself is famously ugly, slimy to the touch, and stinks as it washes up and dries out on beaches and river bends.
The problem has gotten so severe that many municipalities are turning to public service announcements and information campaigns to turn residents off from washing their cars at home. Instead, individuals are advised to rely on their local car wash which, rather than dumping waste water into the local watershed, is required by law to treat waste water and divert it into a local sanitary sewer for proper disposal.
For more information, read this green car wash article by Slate or this recent article by the Washington Post on the related issue of lawn fertilizer runoff.
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