The mineral-medicinal waters come from underground reservoirs, from which they can be obtained via natural springs and upwellings or from artificially sunk wells.
They should have a stable chemical composition, verified using different analyses over time. When these conditions are met and when both its consumption as well as its application to the skin is considered beneficial to health, the Spanish Ministry for Health, with the supervision of the respective Autonomous Regions, can declare the water for public use.
In order for a thermal spa to call itself as such, it should have mineral-medicinal water as well as a medical service and installations appropriate for carrying out treatments. On the other hand, a spa can use tap water, treated or not.
According to the geological characteristics of the area from which the water is taken, it has different substances (mineral salts, gases, sulphuric compounds), in different quantities dissolved in it, which makes it more suitable for treating one problem or another.
Below are the main types of mineral-medicinal waters:
- Bicarbonated: enabling digestion. – Carbonic: benefiting the appetite and regulating the circulatory system.
- Chlorinated: suitable for problems of the locomotor and respiratory system, for the skin, ears and teeth.
- Ferruginous: regenerating the blood, fighting anaemia and good for the skin and for dieting.
- Litinic: beneficial for the skin.
- Radioactive: with analgesic effects and good for combating stress, anxiety and depression.
- Sodium content: stimulating.
- Sulphate content: with laxative and diuretic effects.
- Sulphuric: beneficial for the skin and the locomotory and respiratory system.
According to their overall mineral content per litre (dry residue), they can be of:
- low mineralisation: up to 500 milligrammes per litre;
- medium mineralisation: from 500 to 1,500 milligrammes per litre;
- high mineralisation: higher than 1,500 milligrammes per litre.
The temperature at which the water flows depends mainly on the depth from which it flows, although other factors can intervene. Geologists estimate that hundreds and sometimes thousands of years pass between a drop of rain falling until it flows from a spring in the form of thermal water.