Original: Most car wash facilities are required by law to treat and/or reuse their water and may be required to maintain waste-water discharge permits, in contrast to unregulated facilities or even driveway washing where waste-water can end up in the storm drain and, eventually, in streams, rivers and lakes.
Simplified: Many car wash facilities are now required by law to treat and reuse their water, while driveway wash water simply ends up in the storm drain and eventually into rivers and lakes.