Provided is a water pump including a lower casing, an upper casing coupled to an upper side of the lower casing to form an impeller accommodating space therein by the coupling with the lower casing and having an inlet communicating with the impeller accommodating space and allowing a fluid to be introduced therethrough and an outlet allowing the fluid to be discharged therethrough, an impeller provided in the impeller accommodating space and including an upper plate and a lower plate arranged to be spaced apart from each other vertically and a plurality of blades arranged and coupled between the upper plate and the lower plate, and a rotor coupled to the impeller and rotated together with the impeller, wherein the upper casing has a spacing recess provided on an inner surface corresponding to an outer circumference of the upper plate of the impeller.