Provided are a method for preparing a highly versatile aqueous solution having remarkably improved membrane filterability, which can be stably membrane-filtered in a short time, an aqueous solution prepared by the preparation method, a method for culturing cells using the aqueous solution which is prepared by the preparation method, a method for producing a physiologically active substance using the culturing method, a physiologically active substance produced by the method for producing a physiologically active substance, a method for performing membrane filtration of the aqueous solution which is prepared by the preparation method of the aqueous solution, a method for improving membrane filterability of the aqueous solution, and a method for producing the physiologically active substance by preparing the aqueous solution, performing membrane filtration of the aqueous solution, and then culturing cells using the resulting aqueous solution. The present invention relates to a method for preparing an aqueous solution, characterized by addition of a chelating agent.