The water flows underground from the hills along a fault line called the ‘Penny Quick Fault’ and collects in an underground lake, 2 miles down. The water in the lake gets heated to around 90 degrees C by the earth's core. A tremendous amount of pressure builds up in the lake forcing the water up through a large fissure in the rock allowing it to bubble up to the surface.
The Romans built a reservoir to contain this hot water. By the time the water has travelled the 2 miles up to the surface it has cooled down to 46 degrees C, that’s still about 10 degrees C hotter than a comfortable bath or shower.
After the water had collected in the reservoir the water would have been directed to a number of pools. Today the water only flows into the Great Bath or out of the Great Drain down to the River Avon. Thirteen litres of water flow into the Great Bath every second. This means that you could fill your bath at home in approximately 6 seconds! The temperature of the water in the Great Bath is 36 degrees C, just the right temperature for a bath.
|Point where the water flows into the Great Bath|
|Iron staining on the inflow channel to the Great Bath|
|The green water of the Great Bath|