To provide a method and equipment for treating cooling water, in each of which when a part of the cooling water of a cooling water circulation system for using cooling water circularly is withdrawn and new cooling water is replenished, the withdrawn cooling water is evaporated and volume-reduced by utilizing the calorie of the cooling water of the cooling water circulation system to decrease the load to be imposed on a waste liquid treatment apparatus and make effective use of cooling water.

The method for treating cooling water is used, for example, for cooling the cooling water which is brought into contact with molten slag and whose temperature is raised when molten slag is water-granulated and circularly using the cooled cooling water again as the cooling water for water-granulating molten slag. Namely, this method comprises the steps of: withdrawing a part of the cooling water of the cooling water circulation system; introducing the withdrawn cooling water into a vacuum evaporation part to evaporate the withdrawn cooling water in vacuum by utilizing the heat of the withdrawn cooling water which is brought into contact with molten slag and whose temperature is raised; discharging an evaporation residue to the outside; cooling/condensing the steam generated from the vacuum evaporation part by natural water such as seawater and returning the condensed water to the cooling water circulation system; and cooling the cooling water of the cooling water circulation system, which is made to pass through a heat exchanger of the vacuum evaporation part, by natural water such as seawater to reuse the cooled cooling water as cooling water.

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