Approximately three quarters of Banja Luka is situated in the basin of the Vrbas River, whose 45 km of stream runs through the city, while the rest is in the basin of the Gomjenica River, a tributary of the Sana River. In the territory of the City the most important tributaries of the Vrbas River are the following: Krupa, Švrakava, Suturlija, Vrbanja, Široka rijeka and Dragočajka, while the tributaries of the Gomjenica River are Stratinska, Brkalosa, Bistrica and Piskavička rijeka. Although the basin is rather jagged with a lot of tributaries, rivers and streams, major part of mountainous area of the City is waterless.
Hydropower potential of the Vrbas River is extremely important electrical energy resource in the territory of Krajina. The unused hydropower potential of the Vrbas River, from the existing hydroelectric power plant Bočac until it flows into the Sava River, is approximately 125 MW or approximately 840 GWh of electrical energy, whereof 85 MW or approximately 400 GWh is in the territory of the City.