The Danube flowing across Hungary is a moderately polluted river, at least in its middle stretch, where its greatest polluter is Budapest with 2 million inhabitants and a large industrial complex. Serving the river for drinking water supply, as well, it is obvious that the pollution control for the capital is of paramount importance. There is a 20 year planning concept for the improvement of the sewerage, wastewater treatment and storm water outfall. This long term plan, together with its impact on the water quality of the river and the review of the present conditions, are investigated in this paper.