Fresh water is a finite resource. This is supported by the quantitative review of global water cycle, which suggests a fixed annual volume of water. Fresh water is a natural resource that needs to be maintained by ensuring effective management of water resources. Water is needed for different purposes, functions and services, therefore, water management should be integrated and take account of both demand for and threat to this resource.
This principle assigns a river basin or a catchment area to be a water management unit, which is the so-called hydrographical approach to water management.