Some of the Auvergne's thermal waters naturally contain carbon dioxide, a phenomenon related to the region’s recent volcanic past. Others include mineral salts of great benefit to the human body. The huge variety of our mineral waters here in the Auvergne is due to the high quality of our environment and the exceptional characteristics our volcanic rock and in particular the scoria which do a marvellous job of filtering surface water. As the rainwater passes through the "pozzolanas", the undesirable contents are removed while the water is partly demineralised and acquires numerous rare elements which it picks up along its way. Running beneath the lava, extremely pure mineral waters can be tapped as they emerge. The best example is the Volvic water.