A method for removing humic substances comprising lignin, other lignin type compounds and their disintegration products from an aqueous alkaline waste water from a bleaching of chemical pulp, which method comprises —obtaining an aqueous alkaline waste water comprising humic substances such as dissolved lignin, and —adding a high cationic starch having a charge density value of at least 1.8 meq/g dry matter of starch derivates determined at pH 7-7.5 to the alkaline waste water to precipitate humic substances.