A process for automatically controlling a water treatment process, said water comprising nitrogen and the water treatment process comprising subjecting the water to successive working cycles each comprising at least a carbon oxidation and nitrification stage; and a denitrification stage, the process further comprising in a working cycle - activating aeration means causing aerobic carbon oxidation and nitrification of the water during the nitrification stage, - deactivating aeration means causing anoxic denitrification of the water during the denitrification stage, - dynamically measuring at least a redox potential, ORP, of the water, and calculating a second derivative value d2ORP/dt2 of the ORP from the beginning and during the denitrification stage, this is to say with the aeration means deactivated, wherein the aeration means are activated to end the denitrification stage of the working cycle and to begin a further nitrification stage of a following working cycle only once the d2ORP/dt2 of the ORP reaches at least a third zero value during the said denitrification stage, the process being characterized in that it further comprises the determination of the residual carbon and ammonium in the water after the aeration means are deactivated by measuring the oxygen consumption; and in that the aeration means to begin the further nitrification stage of the following working cycle are not activated to begin the nitrification stage of the next working cycle before an extra period T of "extra-time off", the length of which depends on the previous determined residual carbon and ammonium in the water, has elapsed after the d2ORP/dt2 of the ORP reaches at least a third zero value during the denitrification stage, wherein to measure the oxygen consumption in a working cycle the first derivative value dDO/dt of the Disolved Oxygen DO is calculated during the denitrification stage immediately after the aeration means are deactivated; the extra period T being thus function of the value of the said first derivative value of the DO calculated at the beginning of the denitrification step of the same working cycle. - activating aeration means causing aerobic carbon oxidation and nitrification of the water during the nitrification stage, - deactivating aeration means causing anoxic denitrification of the water during the denitrification stage, - dynamically measuring at least a redox potential, ORP, of the water, and calculating a second derivative value d2ORP/dt2 of the ORP from the beginning and during the denitrification stage, this is to say with the aeration means deactivated, wherein the aeration means are activated to end the denitrification stage of the working cycle and to begin a further nitrification stage of a following working cycle only once the d2ORP/dt2 of the ORP reaches at least a third zero value during the said denitrification stage, the process being characterized in that it further comprises the determination of the residual carbon and ammonium in the water after the aeration means are deactivated by measuring the oxygen consumption; and in that the aeration means to begin the further nitrification stage of the following working cycle are not activated to begin the nitrification stage of the next working cycle before an extra period T of "extra-time off", the length of which depends on the previous determined residual carbon and ammonium in the water, has elapsed after the d2ORP/dt2 of the ORP reaches at least a third zero value during the denitrification stage, wherein to measure the oxygen consumption in a working cycle the first derivative value dDO/dt of the Disolved Oxygen DO is calculated during the denitrification stage immediately after the aeration means are deactivated; the extra period T being thus function of the value of the said first derivative value of the DO calculated at the beginning of the denitrification step of the same working cycle.