In recent years, serious problems have affected water resource which have long been more or less stably maintained. The cause is the changes in the global environment.
Following industrialization and urbanization associated with population growth, energy consumption has increased, causing greater emission of CO2, a major factor in the greenhouse effect, and raising the atmospheric temperature. The extent of the symptoms and the prognosis may not be precisely obtained for the moment, but the direction of these changes is obvious. It is reflected in the decreases in rainfalls, river flows and subsurface water, and saltwater intrusion into subsurface water, as well as in the decline in the residual rate of water resource caused by increasing demand due to the rising air temperature.
These quantitative changes in water resource may be regarded as smaller in effect than the impact of population growth. However, facing further growth of population (estimated at 5 billion for the next half century), the UN Sustainable Development Committee has raised the issue of, "Water resource as one of the greatest problems for the 21st century; i.e. global shortage of water." Furthermore, in 1992, the International Conference on Water and the Environment (ICWE) issued "The Dublin Declaration on Water and Sustainable Development". In 1994, United Nations General Assembly named March 22nd as "UN Water Day", thus beginning to draw people's attention to the forthcoming crisis in water resources.
Although reactions to the water crisis differ between industrialized nations and developing nations depending on regional changes in population and environment, both of them share a common sense of crisis.
