Abstract: A device is described for indicating the depletion of a purifying agent contained in an insert of a water purifying apparatus (7). In order to produce such a device better, to improve it technically, to construct it so as to be user-friendly and also more moderate in price, provision is made according to the invention that an indicator apparatus (1) is arranged in order to indicate to the user the depletion of the purifying agent as a function of the quantity of water which has run through the purifying agent; or alternatively to indicate to the user the depletion as a function of the quantity of water which has run through the purifying agent and as a function of time; in which preferably the indicator apparatus is connected with an arrangement which is arranged on a part (3) movable relative to the insert and which on this movement triggers a switching process.