The water which bubbles up from the ground at Bath fell as rain on the nearby Mendip Hills. It percolates down through limestone aquifers to a depth of between 2,700 metres (8,900 ft) and 4,300 metres (14,100 ft) where geothermal energy raises the water temperature to between 64 °C (147.2 °F) and 96 °C (204.8 °F). Under pressure, the heated water rises to the surface along fissures and faults in the limestone.

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