The elements of the water balance, namely precipitation, runoff, evapotranspiration, and storage change, their interaction and special attributes in the mountains are presented using the example of the European Alps, with particular reference to Switzerland. Strong differentiation in the alpine climate over time and space exerts a significant influence on the water cycle. This chapter therefore discusses each of the elements of the water balance with particular reference to the influence of mountains and their measurement, as well as the spatial differentiation characteristics. The analysis of the water balance is accompanied by a discussion on the attributes and differences at different altitudes and in different climatic regions. Finally, the importance of alpine water resources for water supplies in the adjacent lowlands is examined.