When distilling essential oil, a bi-product of the process is a hydrosol, also known as “flower water,” and is distilled water with many of the fragrance and beneficial attributes of the more concentrated oil. The reason that the hydrosol is perfect for spa treatments is that it can be used directly on the skin, whereas an essential oil should normally be mixed with lotions or creams before topical application.
As many of you know, the scent of lavender essential oil is used in aroma therapy for inducing a relaxed state of mind and has a calming effect on stress. The lavender hydrosol has many of the same fragrance characteristics of the essential oil, but is much less intense. It also can have herbal and grassy notes that make it less like a perfume. Carry a small atomizer for a quick refreshing facial spray. When using hydrosol on the face, be sure to close your eyes and lightly spray several bursts.
Beyond the mentally soothing effect, the hydrosol is also slightly acidic. This makes it a natural antibiotic and is helpful for reducing inflammation and redness associated with various skin disorders such as 
acne, skin rashes, bug bites, minor infections and sunburn. Spray the hydrosol directly on the affected areas and let air dry. https://herbsocietyuk.wordpress.com/2016/01/27/scientific-evaluation-lavender/
The hydrosol spray is useful in balancing the slightly alkaline characteristic of most soaps, bring the pH of the skin back to a natural neutral state. The pH rebalancing also has the effect of toning the face; temporarily tightening skin and fading fine lines. Spray over the entire body after showering or bathing. Spray the hydrosol immediately after facial cleansing and or facial message.
For spa treatments that including soaks, add a half cup of hydrosol along with a half cup of lavender infused Epsom salt to a gallon of warm soaking water. This combination can relieve pain in the hands and feet and soften the cuticles and nails for pedicures and manicures. Soak for at least five minutes.
Like all skin treatments, you should monitor to determine if your skin reacts to too much hydrosol. Using it more than five times per day can undo the beneficial outcomes and lead to redness and/or dryness.