The idea of the realization of this book came during the two years of teaching of the module of hydrology to the students registered in Master I industrial and environmental toxicology at the level of the department of biology at the university chadli bendjedid El Tarf (Algeria). During these years, it was given to me to notice the difficulty of the students to assimilate this course. I hope that the students will find in this book of general hydrology a pedagogical tool to facilitate the comprehension of their field of science. It gives succinct definitions based on an experience of more than fifteen years in the field but also calling upon a rich specialized bibliography.