The paper presents selected causes of problems related to the widely understood phenomenon of secondary contamination of drinking tap water caused by corrosion. The legal aspects, related to the formal responsibility for water quality in water supply systems: cold water and hot water, according to the way it is prepared, have been analysed. The main causes of the deterioration of water quality in water supply systems were characterized by the criteria for assessment of the corrosivity and aggressiveness of the water. Proposals for actions which should be undertaken to prevent secondary water contamination in water supply systems have been drawn up.
