In the distillation process, the water-soluble nutrients are in the hydrosol, where the essential oil captures the oil soluble nutrients. Because the essential oils are not water-soluble they, they want to separate out the water in the separating vat when this is distilled, so then they can siphon off the essential oil. The water that remains in that separating vat is called the "hydrosol." The difference is, first of all, in the aroma. Usually you will see the hydrosol have more of a green or woodier aroma than the oil; or more like the difference between peppermint tea and the essential oil of peppermint. The essential oil has more of a depth to it and the hydrosol does have a very important role to play, because they are gentler than the essential oils. So, for a baby or someone very sensitive, the hydrosol is gentler and safer. It also makes a nice base, even for misting your body and your face. If it seems very light, you could add essential oils to it. For instance, I often recommend people using the hydrosol of rose first on their face while it is still damp. Then use some of the essential oil, which would be in a carrier oil base. Then you have the oil and water-soluble nutrients that were in that plant.
