PURPOSE: To obtain an active carbon free from deterioration of adsorptivity and small in sedimentation velocity by treating a powdery active carbon having equal to or below specific quantity in total acidic group quantity at a specific temp. in an acidic atmosphere to obtain a powder active carbon for water treatment having specific quantity in total acidic group quantity.

CONSTITUTION: The powdery active carbon for water treatment having 15-30 miliequivalent/100g total acidic group quantity by treating the powdery active carbon having ≤10 miliequivalent/100g total acidic group quantity at room temp. to 500°C in the acidic atmosphere. By this method, the powdery active carbon for water treatment free from deterioration of adsorptivity and small in sedimentation velocity by increasing total acidic group quantity and total quantity of the active carbon in an active carbon adding vessel is effectively transferred each time. By treating the active carbon in the acidic atmosphere, oxidation process is simplified.