Water adsorption phenomena are a rich and new field of study in geothermal research, particularly at very high temperatures. ENEL is interested in the exploitation of geothermal regions with superheated steam, so it is important to understand the behaviour of water-rock interaction. We have analysed four samples of Monteverdi cuttings (southwest of Larderello field, Tuscany) in the 170-200 degrees C temperature range and the results are presented in this paper. The presence of adsorbed water is very important, and it is able to multiply the estimated reserves of superheated steam by a factor of 14 in the Monteverdi geothermal field. There is only a slight influence of the reservoir temperature on the amount of adsorbed water.