Analysis of the impact of domestic distribution systems on the dynamics of changes in tap water quality as a necessary element of risk management in the Warsaw Water Supply System - a case study, Poland

The European Parliament adopted the new Directive 2020/2184 on the quality of water intended for human consumption, imposing an obligation on the Member States of the European Union to carry out a risk assessment in the entire water supply chain, from supply areas, to domestic distribution systems. A sensitive area that requires effective risk management by creating appropriate protective barriers based on the procedures of Water Safety Plans, where secondary water contamination most often occurs is the stage of water distribution, both in the water supply network and in internal installations in buildings. The article presents the results of research on secondary water contamination in a large system of collective water supply for the inhabitants of the capital of Poland, Warsaw. The assessment of the daily variability of water quality in terms of microbiological indicators, heavy metals (zinc, copper, nickel, chromium, cadmium), and parameters affecting water acceptability, that is, color, odor, turbidity, and iron and manganese content, showed that the risk of secondary contamination in domestic distribution systems is high. The most common (above 80% cases) and the greatest increase in the concentration of heavy metals in the tap was recorded after overnight stagnation for zinc (average 150%, max recorded concentration 170 µg/L) and copper (average 109%, max recorded concentration 24 µg/L).