Abstract: A system is disclosed for measuring and recording a quantity of liquid in an absorbing material (16), such as the quantity of urine in a nappy, which system comprises a sensor (1) comprising a first pair of electrodes (4, 7) for measuring the quantity of liquid, which first pair of electrodes is arranged to be placed around the absorbing material in, for example, a nappy, and a data logger (10), which is arranged to apply an alternating voltage across the first pair of electrodes and, concurrently herewith, to measure the capacitance between the two electrodes of the first pair of electrodes and to calculate, based on the measured capacitance, an estimate of the quantity of liquid in the absorbing material. In an embodiment, the system further comprises a second pair of electrodes (6, 8) for estimating the presence of a substance, such as faeces, there between using a similar method.