 The water which bubbles up from the ground at Bath falls as rain on the nearby Mendip Hills. It percolates down through limestone aquifers to a depth of between 2,700 and 4,300 metres (8,900 and 14,100 ft) where geothermal energy raises the water temperature to between 69 and 96°C (156.2 and 204.8°F). Under pressure, the heated water rises to the surface along fissures and faults in the limestone. This process is similar to an artificial one known as Enhanced Geothermal System which also makes use of the high pressures and temperatures below the Earth's crust. Hot water at a temperature of 46°C (114.8°F) rises here at the rate of 1,170,000 litres (257,364 imp gal) every day, from a geological fault (the Pennyquick fault). In 1983 a new spa water bore-hole was sunk, providing a clean and safe supply of spa water for drinking in the Pump Room.
