A computer system using regular IC or 3D IC is cooled by using liquid coolants such as water, oil, and ionic liquid. Liquid coolant flows in a closed coolant conduit which is configured to thermally contact heat-generating components in a computer system and a large water body such as river and reservoir. The heat created in computer system is carried out by liquid coolant and dissipated to large water body. The cooling system is simple and cost-effective.