Method for the needs-based metering of ozone or powdered activated carbon, in particular into an ozone/powdered activated carbon reactor of a wastewater treatment or water purification plant, in which the desired elimination efficiency for micropollutants EMV is predefined, the method comprising the steps of: - determining variable values for calculating a required quantity of ozone, wherein, as measured variables, the inflowing quantity of water Q, a UV absorption value UV IN in the inlet of the ozone/powdered activated carbon reactor and a UV absorption value UV OUT in the outlet of the ozone/powdered activated carbon reactor are measured, also further measured variables, which are used to adapt the metering of ozone/powdered activated carbon with regard to the desired elimination efficiency EMV, a nitrite measurement, a redox measurement, a measurement of the residual ozone concentration in the off-gas of the ozone reactor, a DOC measurement and a potassium measurement, wherein from the difference between the absorption values UV IN and UV OUT the value ΔUV is generated, which correlates to the elimination efficiency for micropollutants EMV and which determines the metering of ozone/powdered activated carbon; - calculating the required quantity of ozone or quantity of powdered activated carbon from the variable values and from variable times in which the respective variable values are active, wherein reactions of the ozone or of the powdered activated carbon with substances dissolved in the water are factored into the calculations; and - adapting the metering of ozone/powdered activated carbon using the calculated quantity of ozone or quantity of powdered activated carbon, with the result that amplitudes of the EMV oscillation curve are attenuated and/or damped, wherein when disturbance variables occur, i.e. in the case of fluctuations of the inflowing quantity of water Q, fluctuations of the UV IN value, fluctuations of the substances in the water and/or fluctuations of the water temperature, inside the ozone/powdered activated carbon reactor, which cause the temporal progression curve of the elimination efficiency for micropollutants EMV to oscillate, the effect of a disruption is already detected with reference to a time rate of change of the slope of the EMV oscillation curve before it has an effect in the end result as an under- or overmetering, the metering of ozone/powdered activated carbon is adapted such that the predefined EMV is maintained. - determining variable values for calculating a required quantity of ozone, wherein, as measured variables, the inflowing quantity of water Q, a UV absorption value UV IN in the inlet of the ozone/powdered activated carbon reactor and a UV absorption value UV OUT in the outlet of the ozone/powdered activated carbon reactor are measured, also further measured variables, which are used to adapt the metering of ozone/powdered activated carbon with regard to the desired elimination efficiency EMV, a nitrite measurement, a redox measurement, a measurement of the residual ozone concentration in the off-gas of the ozone reactor, a DOC measurement and a potassium measurement, wherein from the difference between the absorption values UV IN and UV OUT the value ΔUV is generated, which correlates to the elimination efficiency for micropollutants EMV and which determines the metering of ozone/powdered activated carbon; - calculating the required quantity of ozone or quantity of powdered activated carbon from the variable values and from variable times in which the respective variable values are active, wherein reactions of the ozone or of the powdered activated carbon with substances dissolved in the water are factored into the calculations; and - adapting the metering of ozone/powdered activated carbon using the calculated quantity of ozone or quantity of powdered activated carbon, with the result that amplitudes of the EMV oscillation curve are attenuated and/or damped, wherein when disturbance variables occur, i.e. in the case of fluctuations of the inflowing quantity of water Q, fluctuations of the UV IN value, fluctuations of the substances in the water and/or fluctuations of the water temperature, inside the ozone/powdered activated carbon reactor, which cause the temporal progression curve of the elimination efficiency for micropollutants EMV to oscillate, the effect of a disruption is already detected with reference to a time rate of change of the slope of the EMV oscillation curve before it has an effect in the end result as an under- or overmetering, the metering of ozone/powdered activated carbon is adapted such that the predefined EMV is maintained.