The experiments were conducted on full scale at the Mont-Valérien treatment plant treating the Seine river downstream from Paris. Over one year, the efficiency of different types of full-scale slow filters (sand, sand +granular activated carbon (GAC), with and without preozonation) and pilot scale rapid GAC filters with preozonation were compared. Slow sand filter remove an average of 10% TOC primarily through biodegradation. Slow GAC remove an addi-tionnal 15% TOC primarily through adsorption. The total reduction is thus 25%. Ozone removes 5% but does not enhance GAC performance.