Method of processing data obtained by operating a liquid treatment system including a liquid treatment part (4;26;62) containing at least one liquid treatment medium, which method includes: receiving a measurement signal, values of which are representative of a first parameter, the first parameter being a parameter of the liquid depending partially on a concentration of at least one component removable to at least some extent by the liquid treatment part (4;26;62) from liquid flowing through the liquid treatment part (4;26;62) and also on that of other components that are not removable, wherein the signal is a signal originating from a sensor (12;33;57) located downstream of the liquid treatment part (4; 26; 62); determining values of the measure of the concentration of components removable by the liquid treatment part (4;26;62) on the basis of at least respective values of the measurement signal; and determining values of at least one second parameter, each second parameter corresponding to an integral of a variable from a point in time at which liquid treatment medium in the liquid treatment part (4;26;62) is in an initial state over periods during which liquid flows through the liquid treatment part (4;26;62), wherein the variable is at least dependent on one of a rate at which liquid flows through the liquid treatment part (4;26;62) during use and a rate at which liquid flows through the liquid treatment system during use, characterised by at least one of: (i) determining whether to provide a value of the measure obtainable on the basis of at least a current value of the measurement signal as input for a further process; and (ii) adapting the determination of values of the measure in dependence on a current value of at least one of the second parameters. receiving a measurement signal, values of which are representative of a first parameter, the first parameter being a parameter of the liquid depending partially on a concentration of at least one component removable to at least some extent by the liquid treatment part (4;26;62) from liquid flowing through the liquid treatment part (4;26;62) and also on that of other components that are not removable, wherein the signal is a signal originating from a sensor (12;33;57) located downstream of the liquid treatment part (4; 26; 62); determining values of the measure of the concentration of components removable by the liquid treatment part (4;26;62) on the basis of at least respective values of the measurement signal; and determining values of at least one second parameter, each second parameter corresponding to an integral of a variable from a point in time at which liquid treatment medium in the liquid treatment part (4;26;62) is in an initial state over periods during which liquid flows through the liquid treatment part (4;26;62), wherein the variable is at least dependent on one of a rate at which liquid flows through the liquid treatment part (4;26;62) during use and a rate at which liquid flows through the liquid treatment system during use, characterised by at least one of: (i) determining whether to provide a value of the measure obtainable on the basis of at least a current value of the measurement signal as input for a further process; and (ii) adapting the determination of values of the measure in dependence on a current value of at least one of the second parameters. (i) determining whether to provide a value of the measure obtainable on the basis of at least a current value of the measurement signal as input for a further process; and (ii) adapting the determination of values of the measure