Method for controlling a water treatment installation having a supply, an ozonization stage, a transfer stage, a biological filter and a discharge having the following steps: measuring a first parameter set in the supply, wherein, a measurement for a first concentration of micro-contaminations and/or a nitrite concentration is determined; controlling the ozonization stage in such a manner that an ozone supply is carried out in a preselected ratio to the measured first parameter set; measuring a second parameter set in the transfer stage, wherein, a measurement for a second concentration of micro-contaminations is determined; controlling the ozonization; measuring a third parameter set in the discharge, wherein, with reference to the third parameter set, a measurement of a third concentration of micro-contaminations is determined; if the measurement for the concentration of micro-contaminations exceeds a predetermined maximum value in the discharge, increasing the ozone supply.