This is the only thermal water spring in the Balearic Islands.
Although it has probably been known since Roman times, the first reference to its use is in the 16th century. The present-day spa dates from 1844.
The spa uses the waters for therapeutic purposes. They are sodic chlorinated waters with a certain natural radioactivity that makes them unique
A) View of the main façade of the spa, B) Inaugural plaque of the amenities. C) One of the thermal water fountains.
The origin of this natural emergence of hot water is related with the geothermal anomalies of the eastern sector of Mallorca.
The water comes from an aquifer situated at a depth of more than 1000 metres which, due to the geothermal gradient of the Tierra, has a temperature of 85ºC. This water, which in principle should be confined, wells up towards the surface through a fault. As it rises, it mixes with the waters of other aquifers, changing its composition (some aquifers carry saltwater and others freshwater) and temperature. The resulting water emerges at the surface at a temperature of some 38 degrees, highly mineralised and of a brackish nature, characteristics that give it its special properties.
Geological diagram of the spring of Sa Font Santa de Sant Joan. The green-coloured materials are impermeable while the rest are permeable and include aquifers. The fault allows the water to well up, becoming mixed before it reaches the surface. Modified from Mateos Ruiz & González Casasnovas (2009).
As a curiosity we can add that in the spa’s buildings, mostly constructed in marès rock, there are blocks in which hoofprints of Myotragus can be seen in cross-section. Myotragus was an autochthonous bovid of the Balearic Islands, now extinct.
Block of marès with a vertical section of a hoofprint of Myotragus (convex shape in the centre). Originally, this block of marès would have been in an inverted position, because the direction of the hoofprint is logically downwards and not
Near the spa is the church of Sant Joan de Sa Font Santa and an old cistern from the 17th century which supplied drinking water to the spa until the end of the 20th century, in view of the scarcity of water in the region.
A) Exterior view of the cistern and B) detail of its interior.
