In a refinery, crude containing high levels of salt will go through a desalter before being fed to the atmospheric distillation tower.

In the desalter, the crude oil is mixed with 5-15% volume of fresh water so that the water can dissolve the salts. The oil water mix is put into a settling tank to allow the salt-containing water to separate and be drawn off. Frequently an electric field is used to encourage water separation.

Removal of salts is important for reducing corrosion in the distillation tower and downstream processing units.