[Object] The object of the invention is to provide a granular antimicrobial agent for water processing which has sufficient water permeability and antimicrobial effect, and the effective duration of which can be readily ascertained when used as a water-processing antimicrobial agent in the home.[Means for Solving the Problems] A granular antimicrobial agent for water processing which has a solubility at 25° C. of preferably 0.1 mg/g·L·hour to 1 mg/g·L·hour, comprises 0.5 wt % to 4 wt % of Ag2O, 2 wt % to 10 wt % of K2O, 35 wt % to 50 wt % of SiO2, and 40 wt % to 55 wt % of B2O3, and has a semispherical or conical shape in part was found. In addition, the inventors found that the antimicrobial agent is highly suitable for use in various kinds of water processing, particularly, the antimicrobial treatment of water used for washing, and completed the invention.
