PURPOSE: To manufacture inexpensively safe and healthy drinking water by manufacturing a plant by utilizing oxidative and sterilizing action of hydrogen peroxide as a method for sterilization and clarification in water purification plant and facilities.

CONSTITUTION: A raw water (a city water) is purified by removing suspended substances, emulsified substances and other impurities in the water by means of active carbon treatment and then, hydrogen peroxide is automatically injected into the obtd. purified water in accordance with the quality of the raw water. While the raw water wherein hydrogen peroxide is injected is stirred, then, manganese dioxide powder is mixed or it is passed through a particulate manganese dioxide layer. Manganese dioxide is a decomposition catalyst for hydrogen peroxide and as hydrogen peroxide is turned into water by producing oxygen with a strong oxidative and sterilizing power when it is decomposed, sterilization of the raw water can be performed by this action. In addition, the time for bringing hydrogen peroxide into contact with the decomposition catalyst is controlled so as to keep sterilizing force of the hydrogen peroxide and to make it possible to use semi-permanently the decomposition catalyst.