Hydrosols are the pure natural floral waters or distillates only produced through steam, hydro or hydro/distillation; Water is needed for a hydrosol to occur. Hydrosols are like essential oils but in far less of a concentration.
The plant material is placed into the retort (still) or distillation tank. The steam hits the plant, the water boils the material softening the scent or secretory cells releasing the essential oil that is contained within as a vapor. This essential oil vapor mixes with the steam and is separated again as the steam cools in the condensing tank. As the steam cools, the essential oil molecules separate from the steam (now as cooled water) and float on the water (except for the very few of them which sink) and the water, now is called the hydrosol, (sometimes referred to as the hydrolat) is syphoned off.
The highest quality hydrosols come from the devoted artisan distillers who, with artist-like precision, steam the floral and plant material strictly to produce a hydrosol. Hydrosols contain all of the essence of the plant in every drop, just like essential oils but in a milder form; making them suitable for all manner of applications where essential oils would be too strong.