Water resource problems at regional and global scales fall within the sphere of activities of many international governmental and non-governmental organisations such as UNESCO, WMO, UNEP, FAO, IAHS, IWAR and others, all of whom have sponsored numerous scientific conferences and symposia to focus on these problems. An enormous quantity of studies have been published in many different countries, with perhaps the most complete and detailed estimates of the water balance and water resources for all the continents and the Earth's natural geomorphologic zones published in 1974. Based on close international co-operation, these figures were obtained by Russian scientists under the guidance of the State Hydrological Institute and cited in the monograph World Water Balance and Water Resources of the Earth, Baunmgartner and Reichel (Germany) also presented similar estimates in 1975 in the monograph World Water Balance.

The data in both these monographs have been widely used by scientists ever since as the most comprehensive and reliable data sources, as no subsequent publication dealing with global water data has produced any new information, even for those countries with ample scientific facilities. Further, the reliability of data is not considered to be very high because it comes from different sources, including obsolete methods for obtaining readings, sometimes even relating to different years or other long-term periods. It was in this context, therefore, that UNESCO established a new project within the International Hydrological Programme to standardise the world's data on water resources and their uses and to prepare a monograph World Water Resources by the beginning of the 21st century. The State Hydrological Institute at St Petersburg, Russia, was charged with carrying out the project during 1991-96.

This executive summary introduces the reader to the basic results and inferences made during the project
and preparation of the monograph.