The basic principle of WHYCOS data policy is that countries are the owners of the data they generate and their NHSs are responsible for the checking and validation of this data in accordance with national regulations. To enable participating countries to perform this basic task is therefore a priority in the project implementation to establish the necessary data transmission and management infrastructure and create the required human capacity in the NHSs involved.

Strengthening regional cooperation on water related issues is one of the main objectives of each HYCOS component. As a preliminary step toward this goal, the data from the HYCOS stations of each component should be shared among the participating countries to meet regional and international requirements and pursue common development objectives. Such an exchange is to be done in accordance with the internationally agreed policy framework contained in WMO's resolutions 40 (Cg-XII) - WMO policy and practice for the exchange of meteorological and related data and products - and 25 (Cg-XIII) - Exchange of hydrological data and products, on the international exchange respectively of meteorological and of hydrological data and products.

Another WHYCOS main objective is to promote global data exchange and scientific cooperation. Moreover, project generated data and information are also contributed to the global data centres operating under the aegis of or in cooperation with WMO, such as GRDC, GPCC and GEMS-WATER

A key element for facilitating this exchange of data and information is the establishment of hydrological information systems, using the Internet and other modern data transmission technologies. Such systems provide a medium for easy, fast dissemination and exchange of water-related data and information. Participating Hydrological Services establish sites on the World Wide Web to enable easy access to selected information. Raw data are usually available in near-real time, although the service responsible for each monitoring station will subsequently carry out data quality assurance, according to WHYCOS criteria of data standards and timeliness. Derived products, such as maps of specific runoff, may be subject to cost recovery for the hydrological services.