Hydrosols, also known as spiritous or aromatic waters, are lovingly referred to as the co-product of the distillation process, alongside essential oils, which sit either on the surface of the water or settling on the bottom underneath the aromatic water. Citrus oils are lighter while Vetiver and Patchouli tend to land on the bottom.
Though hydrosols are in some way considered the inseparable qualities of oil and water, it is still necessary to separate the essential oil from the aromatic water. This happens either by using a separatory funnel or with a pipette, which is absolutely fiddly and in my experience, rather imperfect.
The plant material is placed in a pot with water, and when steam distilling, the plant material is placed in the column that sits over the water. This would be referred to as Hydro/Steam Distillation.
Contained impeccably, so as not to let any steam escape, the water is heated slowly. As the plants open with the heat, their pockets of potent essential oil molecules are released, and they begin to rise up, liberated within the steam, to then cool and fall, condensing into an alchemized liquid state.