A water-based coolant contains: at least one inorganic acid salt selected from among carbonate, hydrogen carbonate, sesquicarbonate, phosphate, borate, molybdate and tungstate; and a metal corrosion inhibitor. The water-based coolant is excellent in cooling performance and unlikely to cause corrosion of a metal material to be cooled. Therefore, the water-based coolant is suitably usable as a quenchant or a cutting oil.