The design of hydrological networks takes place between the field of the phenomena to be measured on the one hand and the needs to measure on the other hand. Apart from a classification of the networks according to the variables to be measured one can distinguish the networks according to their objective, going from short term objectives, such as forecasting and operational management of water projects to long term objectives, such as trend detection. Again another distinction can be made in networks for water quantity and water quality data.

Water is essential to life for humans and their food crops, and for ecosystems. Effective water management requires tracking the inflow, outflow, quantity and quality of ground-water and surface water, much like balancing a bank account. Currently, networks of ground-based instruments measure these in individual locations, while airborne and satellite sensors measure them over larger areas. Recent technological innovations offer unprecedented possibilities to integrate space, air, and land observations to advance water science and guide management decisions. This book concludes that in order to realize the potential of integrated data, agencies, universities, and the private sector must work together to develop new kinds of sensors, test them in field studies, and help users to apply this information to real problems.