Approximately for 300 years on land there was a huge network of supervision of water objects and components of circulation of water. more than 150000 of measurements of deposits, 60000 stations In this network, measuring the charge of water on the rivers, 10000 stations, measuring evaporation. On thousand of stations a level of water, quality of water and the ice phenomena are measured. On other thousands of stations the supervision over underground waters, fluctuations of a mirror of water in layers carrying water, chemical structure of underground waters is conducted. On coast of the seas the supervision over changes of its level are conducted, and hundreds of ships will carry out complexes of various supervision in ocean of waving, currents, saltiness, temperature of water, and ground adjournment. The work of all these stations and ships is closely connected to a network of meteorological supervision, which gives the large additional information.

If the ancient hydrologers and hydrotechners had only some practical knowledge and intuition, now hydrological science and practice are based on an extensive observant network on land and on the sea, huge number of research ships, network of meteorological stations, deeply developed theory of circulation of water and model of a mode and dynamics of water in various water objects. Network of supervision contains systems based on the newest technology: electronics, computer engineering, telecommunications. The example is the artificial satellite of the Earth. They are used in two directions. In one case the various devices, established on them, can collect the extensive information: to define the humidified and dry surface, type of a vegetative cover and phases of vegetation, distribution of a snow cover, zone of flooding, strong waving, place of origin and trajectory of movement of tropical hurricanes, temperature of a surface of ocean, lake, rivers and so on. Thus the information turns out at once for extensive territory, for most removed and daring parts of our planet. In the other case the satellite can be used as the device for "interrogation" of a ground automatic network of stations of supervision, accumulation and transfering of this information to the centres of its processing, storage and distribution.

Huge volume of the hydrological information is used first of all for development of the forecasts and warnings of the dangerous spontaneous phenomena on water objects of a land and on the sea: floods, droughts, jams of ice, ice conditions by the seas, wavings, tsunami, tropical hurricanes, motions of glaciers. The forecasts are given not only with the purpose of prevention of damage and accidents. The forecasts of the phenomena and condition in hydrosphere are used for planning economic tasks. Other field of use of the given network of supervision is an estimation of water resources for various territorial units - from water objects and river pools up to the states and continents. At last, the data of supervision are widely used for accounts at designing and construction of economic objects, as practically any object can not manage consumption in that or other volume of water. These data are especially important for objects which are directly connected to elements of hydrosphere of water fences, bridges, dams, dams, port structures, hydroelectric power stations, as they are the largest consumers of water for cooling mines, pipelines and so on.