Water purification agent and water purification method

A water purification method, comprising:

• obtaining the water purification agent by:
• a) grinding a dried plant to obtain a plant powder having a number average particle diameter of 250 μm or less;
• and
• b) mixing the plant powder with a polymer coagulant, adding water to the plant powder and the polymer coagulant, kneading the plant powder and the polymer coagulant, and subjecting a resultant to extrusion granulation to obtain the granulated product;
• wherein the water purification agent comprises the granulated product,
• wherein the granulated product comprises a mixture of the plant powder and the polymer coagulant,
• obtaining a dispersion liquid in which the plant powder and the polymer coagulant are dispersed in an automated supplying machine, and
• feeding the dispersion liquid to wastewater to remove an unnecessary inorganic substance in the wastewater in an automated purification device;
• wherein a bulk specific gravity of the water purification agent is 0.4 g/cm3 or greater;
• and
• wherein variation of the bulk specific gravity of the water purification agent is 4.5% or less, where the variation is a ratio of a difference between a maximum and a minimum of the bulk specific gravity to the minimum of the bulk specific gravity.