The volatile compounds are extracted from the plant material by various methods of distillation and held in sealed containers. Herbal extracts are the dissolving of compounds found in the herb by means of solvents, usually an alcohol and water combination. Many herbs do not contain essential oils, and this method extracts the beneficial substances found in the plant. Herbal extracts and essential oils contain actives which can aid in stress reduction when made available to the body in the water bath. In natural thermal pools there are many dissolved minerals found which also have a strong therapeutic effect.
Minerals play an important role in water conditioning.
In order for the body to benefit from the essential oils and herbals used in the bath they must be uniformly dispersed in the bath water. Soft water, or water deactivated of dissolved metals like iron, calcium, and magnesium are the most ideal for a full dispersion of the botanicals. Natural sodium minerals like sodium borate, sodium carbonate, and sodium chloride neutralize metals and also set up a mild electrolyte solution which helps attract the botanical molecules to the skin. Hard mineral water keeps the botanicals out of solution and away from the body. A surface scum or ring around the tub is often a sign of hard water.