A water jacket apparatus for an engine may include a block water jacket provided in the cylinder block, interposing the combustion chamber therebetween, a head water jacket provided in the cylinder head corresponding to the combustion chamber, and an insert member portioning the block water jacket into an upper block water jacket and a lower block water jacket by being inserted into an upper portion of the block water jacket, and enabling the upper block water jacket to be interworked with the head water jacket.