Hydrosols are the pure co-product of the steam distillation of plant material. When plants are steam distilled to produce essential oils, some valuable compounds of the plant, that are not found in the essential oil, become dissolved in the distillation water.

This condensed fragrant steam is known as hydrosols or aromatic waters. It contains some drops of the essential oil as well as water soluble plant properties which are anti-inflammatory and non-irritating for sensitive skin. The micro drops of essential oil provide the scent and taste. The plant components give the hydrosols their herbal therapy properties. Hydrosols are gentle yet powerful therapeutic agents in their own right.

Note:
No essential oils are collected from this hydrosol, leaving the volatile oils and other valuable constituents contained within the hydrosol.

These compounds give the hydrosol the therapeutic actions of the plant, in a gentle yet powerful medium.

(Excerpt from Go Native)