An aromatherapy hydrosol is scented water produced during the process of steam-distilling plant material to produce essential oils. These aromatherapy waters have some of the same benefits as essential oils but are more gentle, and you can sometimes use them when essential oils aren't advisable.
Also, some distillers focus only on producing these plant waters (also called hydrolates, hydrolats, or distillates), without producing essential oils. You might sometimes hear the terms floral waters or flower waters, but they aren't the same as distillates and don't have the same benefits.
Possibly the most definite book available on this topic is Suzanne Catty's Hydrosols: The Next Aromatherapy.
Just as you want to use the best quality essential oils for maximum benefit, you also want to use the best quality distillates. Aromatherapy waters are more easily contaminated in the production and shipping process than essential oils, so finding reputable suppliers is important.
Plant waters are also more fragile than essential oils and don't last as long. Storing the waters in a dark, cool place will prolong their life. Although some plant waters contain preservatives, purists believe preservatives lower quality.
Another important thing to know is that mixing essential oils and water together doesn't create a distillate. So, if you are looking at a floral water, for example, rose water, and the ingredient list is purified water and natural rose oil, it's not a hydrosol and doesn't have the same properties. (That's not to say that rose water isn't sometimes useful.)
Other products on the market that may not be real distillates are fruit-scented waters (orange, lemon, and so forth). Fruit essential oils are most often cold-pressed (with a few exceptions) from fruit skins, not distilled, so no aromatherapy water is produced. Another example is jasmine; this oil is solvent-extracted, not distilled, so, again, no hydrolat.
One use of aromatherapy waters is in making natural lotions, creams, and other skin care products. The following chart shows some more common distillates and their use in skin care.
Cornflower (Centaurea cyanus)
Cypress (Cupressus sempervirens)
Geranium (Pelargonium graveolens)
Helichrysum (Helichrysum italicum)
Melissa (Melissa officinalis)
Neroli (Citrus aurantium)
Rose (Rosa spp.)
Rosemary (Rosmarinus officinalis) verbernone
Sandalwood (Santalum album)
Yarrow (Achillea millefolium)
Baby, delicate skin
Eczema and other inflammation
All skin types; also for inflammation
Baby, delicate, and mature skin
Baby, delicate skin and inflammation
Balancing and for oily skin
To balance & calm; for inflammation
You can freely drink therapeutic-grade aromatherapy waters. Although Catty provides many suggestions for internal use, the topic is too big to get into in this article. Here's a recipe she recommends for headaches: