The hydrology of Hungary, is mostly determined by Hungary's lying in the middle of the Carpathian Basin, half surrounded by the Carpathian Mountains. All parts of the country have some outflow. All surface water gravitates towards its southern center, and from there, is united in the Danube, which flows into the Black Sea. The whole of Hungary lies within the Danube drainage basin.
The total length of all the irrigation systems and inland waterways in the country is about 26,000 km (16,000 mi).
The annual water balance of the country shows a surplus. Yearly about 100 km3 (3.5×1012 cu ft) of water leaves the country towards the Black Sea. From that, precipitation amounts for only 10%, the rest being provided by the incoming rivers of surrounding countries.