Thermal water and thermal springs
Thermal water is a special form of groundwater. If groundwater is highly mineralized and has a high temperature, it is thermal water.
Aachen's thermal water is deep water that obtains its high temperature and mineralization by rising from a depth of up to 3,000 m. It is formed from rainwater that rains down and seeps away. It is formed from rainwater that rains down and seeps away in the Aachen South / High Fens catchment area. Over a long period of time, the infiltrated water penetrates deeper and deeper into the subsoil until it reaches impermeable layers. According to the hydrostatic gradient, it flows in the direction of the Aachen basin and finally reaches the surface in the thermal springs. The thermal springs are bound to a specific limestone formation (Devonian limestones of the Frasnes Formation) and emerge in two elongated areas along the Aachen and Burtscheid thrust faults in Aachen city center and in Burtscheid. The water has an age of approx. 10,000 years and an outlet temperature of approx. 38 - over 70°C after passing through the underground. The Aachen springs are therefore among the hottest thermal springs in Central Europe and have a high degree of purity due to their genesis.
The city name Aachen is probably derived from the Celtic or Old Germanic "Ahha" or from the Latin "aqua" and means something like "water". In this sense, Aachen, like many other cities, was founded on water; not on the river, however, but on the hot, mineral and sulphurous springs. The Romans also used the springs for bathing and recreational purposes. The springs were (and still are) said to have a healing effect, e.g. for rheumatic diseases. It was also for these reasons that Charlemagne established Aachen as an important city.
In the course of time, around 30 different springs or spring forebays were known and there was a rich tradition of spas and bathhouses. Many of the springs no longer exist today (buried, built over, etc.). Today there are still 15 accessible springs, of which six are active and nine are unused or inactive, i.e. without water extraction. The extraction of water from the active springs lowers the water level in the entire limestone range; there are no longer any free-flowing springs. Originally, the thermal springs were artesian springs, i.e. they flowed out naturally on the surface.
Of the six active springs, three are operated by the City of Aachen, two by private users and one is discharged. A permit under water law is required for any use of water (thermal water is groundwater). There are elevated permits for the Aachen thermal springs. The quality of the thermal water is monitored by the Lower Water Authority through regular analyses. Analysis of the Kaiserquelle
The three municipal thermal springs are also subject to pharmaceutical law, as the springs are state-recognized medicinal springs and the city of Aachen has a manufacturing permit under pharmaceutical law for the springs as a medicinal water company.
As in times gone by, the thermal water is mainly used today for spa and bathing purposes. The Carolus Thermen, which uses the water from the Rosenquelle-Komphausbadstraße, and the spa clinics in Aachen-Burtscheid are particularly well-known.
There is also a thermal water fountain in Aachen and Burtscheid, where the thermal water is accessible to the public in its unaltered form. In Aachen's city center, this is the Elisenbrunnen fountain and in Burtscheid on the market square it is the Marktbrunnen fountain.