In today's modern car wash facilities, whether tunnel, in-bay automatic or self-serve, soaps and other cleaning solutions used are designed to loosen and eliminate dirt and grime. This is in contrast to earlier times, when hydrofluoric acid, a hazardous chemical, was commonly used as a cleaning agent in the industry by some operators. There has been a strong move in the industry to shift to safer cleaning solutions. 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 (at one's home), where waste-water can end up in the storm drain and, eventually, in streams, rivers and lakes.
The car wash will typically start cleaning with chemicals called presoaks applied through special arches. These arches often use nozzles positioned to spray chemicals in a bi-directional pattern. In many cases, presoak arches are designed to foam the presoak prior to its application to the car. They may apply a higher pH (mild alkali) followed by a lower pH (mild acid), or the order may be reversed depending on the car wash operator's preference. Chemical formulas and concentrations may also vary based upon seasonal dirt and film on vehicles, as well as exterior temperature, and other factors. Chemical dilution and application works in combination with removal systems based on either high pressure water, friction, or a combination of both.