Geothermal heating a total capacity of 15 GW extracted 88 PJ of heat energy for space heating. Global ground-source heat pump capacity is growing by 10% annually. Hot springs have been used for bathing at least since Paleolithic times. The oldest known spa is a stone pool on China's Mount Li built in the Qin dynasty in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. Geothermal energy supplied channeled district heating for baths and houses in Pompeii around 0 AD. In the first century AD, Romans conquered Aquae Sulis in England and used the
Albulae Aquae Albulae Aquae Albulae Aquae ("The White Water") is a group of springs located West of Tivoli in Italy. The springs' water is bluish, strongly impregnated with sulphur and carbonate of lime, and rises at a temperature of about . The remains of a Roman thermal establishment exist near the principal spring, the so-called Lago della Regina, which is continually diminishing in size owing to deposits left by the water. Dedicatory inscriptions in honour of the waters have been found at the site. It is mentioned briefly by many ancient authors, among them, Virgil, Vitruvius, Isidore of Seville, and Pliny the