This invention relates to process for preventing both corrosion and the formation of scale in water- conducting systems which comprises adding a zinc carbonate and hydroxyl ethylene diphosphoric acid (HEDA) to water. The main problems arising in hydraulic engineering, e.g. when untreated water for cooling purposes are the occurrence of corrosion and the formation of scale. The corrosion of metals such as steel, copper and alloys of these metals which commonly used for water circulation tanks is mainly due to the action of oxygen, carbon dioxide ,chloride gas , chloride ions and many others ions dissolved in the water. The prevention of corrosion by forming thin film of complex HEDA and zinc ions which actions with corrosion ions while the prevention of scale by forming heat stable soluble complexes with calcium and magnesium.