A hydrosol is a water-based botanical extract produced from the steam distillation of aromatic flowers and herbs.
During the distilling process, fresh or dried plant matter is placed inside a copper vessel with purified water. The vessel is sealed and heated to 200F in order to generate steam that will break down the plant's cellulose. Once the cellulose is sufficiently weakened the plant's water and oil soluble chemical constituents escape and are carried away by the steam. The steam then enters a cooling coil and condenses back into liquid form and is collected inside of a receiving container . As this liquid extract settles, the essential oil separates and floats to the top while the hydrosol settles to the bottom.
The resulting distillate will contain about 2%-5% essential oil and 95%-98% hydrosol. Some common examples of hydrosols are rose water and orange blossom water.