It is an object of the present invention to provide an indication of the state of health of an individual by monitoring changes in one or more characteristic constituents or properties of urine. In particular, the present invention provides an indication of the state of hydration of an individual with, preferably, the aim of determining any type of hydration imbalance. In order to achieve such indication of the state of health of an individual, the present invention provides a device or system capable of measuring conductivity and using such conductivity to estimate the volume of each micturition event.