Steam distillation is the most popular method for extracting oil from plants; the process involves heating the water to produce steam. An outside source of steam is used, which is introduced into the distillation unit at a high pressure. The steam is finally condensed and the resulting essential oil or extract is left. 

Water and herb are put together into a pot and heated until the temperature reaches a point where steam is formed. The steam will evaporate to enter the column part of the still and then the condenser to return to a liquid form. Herbal compounds that enter the distillate portion include a mixture of essential oil and water. These herbal distillates are often called herbal waters or hydrosols.