Are hot springs all natural？

Hot spring is naturally exposed underground hot water. As regulated in China's national standards， hot water temperature above 25℃ can be called hot spring. Natural hot springs contain warm springs， hot springs， pot， boiling fountains， jet stream， mud springs， boiling mud springs， etc. The concept of hot springs is extended in the modern business and it also refers to the underground hot water which is artificially drilled out. Beijing did not have hot springs in the past， but after exploration and drilling of geothermal experts， 500 water hot springs were drilled out with underground hot water. Now the deepest hot spring in Beijing reaches 4，040 meters underground. In Beijing， more than 70 hot springs are used for leisure and holiday resorts， etc.

（Answered by Zheng Keyan）