The effectiveness of car washing management practices at reducing nonpoint source pollutant loads has yet to be measured accurately. Due to the diffuse nature of nonpoint source pollution, it is often difficult to determine the exact impact of a particular pollution prevention measure at reducing pollutant loading.
While not much is known about the water quality of car wash water, it is very clear that car washing is a common watershed behavior. Three recent surveys have asked residents where and how frequently they wash their cars. Results are provided in the table below.
|Smith, 1996 Maryland
||60% Washed car more than once a month
|Pellegrin, 1998 California
||73% Washed their own cars
73% Report that wash water drains to pavement
|Hardwick, 1997 Washington
||56% Washed their own cars
44% Used Commercial car wash
91% Report that wash water drains to pavement
56% Washed car more than once a month
50% Would shift if given discounts or free commercial car washes