This photo illustrates the holistic nature of many water problems: the river (or groundwater) provides the city with water for its many uses, while at the same time acting as the recipient for its waste, which eventually is carried to the sea. The quantity and quality of the river or groundwater varies over time, depending on both natural variations (possibly affected by climate change), and on effects of human activities upstream, not least agricultural practices. Coastal problems often find their solution in the upstream land use, or in the practices of the city; while management of water and waste for people, businesses and industries in the city calls for the ability to act in response to often rapidly occurring changes. Many of these problems require technologically based, holistic approaches.