, is a term used to denote all the waters found beneath ground surface. However, groundwater hydrologists, who are primarily (but not exclusively) concerned with the water contained in the zone of saturation (Subs. 1.1.1), often use the term ‘groundwater’ to denote water in only this zone. In this book, we adhere to this definition, using the term
the water below ground surface. Practically, all groundwater can be regarded as part of the hydrological cycle (Fig. 1.1.1; or see any textbook on Hydrology). Very small amounts, however, may enter the cycle from other sources (e.g., magmatic water).