Why take your car to the wash when you can wash it home for free? Believe it or not, washing your car at home can have much more impact on local water supply and surface water quality than you would think.

The average at-home wash uses about 150 gallons of water. A typical automatic car wash uses anywhere from 50 to as little as 15 gallons of water for the same (or better) wash. Multiply that savings by the many thousands upon thousands of car washes in San Mateo County each year, and the water savings from using a local car wash over your driveway become clear.

From a water quality standpoint, washing a car in your driveway can have similarly negative impacts. The rinse water that runs off your driveway will flow into a storm sewer and, in most cases, directly to the Bay. That rinse water contains the soaps used in washing with high levels of phosphates. These can contribute too much nutrients to local waters and cause algae blooms in the Bay. Brake dust and oils are also washed off of cars, which can contain heavy metals including lead.

Conversely, almost all car washes are now required to extensively filter (and sometimes recycle) the water that is used in the washing process. The water that is discharged is sent into the municipal sewage treatment system and not the Bay.

Researched by Kimberly Siu

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