From the Eden Botanicals website: Hydrosols are the aromatic waters that occur as a co-product of Essential Oil distillation. There are a number of other (and some less than accurate) names for these: hydrolats, floral waters (although they are obtained from more than just flowers), herbal waters, etc. Also, authentic hydrosols are not to be confused with products made by combining Essential Oils or Absolutes with plain/distilled water. There are as many hydrosols as there are Essential Oils, and as awareness of their potential increases, we see many more diverse hydrosols become available due to the demand for them.
In the distillation process, plant material is either subjected to steam or is immersed in boiling water, or both. In any of these cases, the heat causes the cells of the plant material that hold the Essential Oil to soften and release their contents. This oil is volatile and rises as a vapor with the steam into cooling tubes, from which two products result - the Essential Oil, and the steam that cools (condenses) into water. The condensed cellular water of the plant - known as the hydrosol - contains many components and includes the water-soluble (hydrophilic) micro-molecules of some of the components found in the Essential Oil of the plant.
According to Kurt Schnaubelt in his book Medical Aromatherapy - Healing with Essential Oils, aromatic hydrosols provide an elegant alternative and are "eminently useful for aromatherapy treatments, especially for children, when the use of the Essential Oil might be too strong." Also, many constituents in hydrosols are different from those found in the Essential Oil from the same plant material. As such, while hydrosols may have actions similar to their Essential Oil counterparts, they may have other attributes their Essential Oil counterparts would not.
Suzanne Catty, author of Hydrosols - the Next Aromatherapy, states: "…hydrosols can be seen as micro-doses of [essential] oil" and, when further diluted in water, become akin to homeopathic in their action. This is one of the reasons why the gentleness of hydrosols is ideally suited in the delivery of their attributes for children, the elderly, and those with pronounced sensitivities. They are also a profound and delightful way to experience and appreciate the life force - with all its potentiality for wholeness - found in the aromatic waters of the plants.