A computer system using 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 thermally to contact heat-generating components and a liquid-liquid heat exchanger. The heat generated in 3D IC chips is carried out by liquid coolant and dissipated to heat exchanger where cooling water dissipates heat to large water body. For economic stable operation, cooling water is pumped from large water body such as river to a water tower where water level is kept constant to ensure heat exchanger work at optimal condition. The simple approach for computer system cooling provided in this disclosure is a cost-effective data center efficiency solution.