Presented herein are systems and methods for measuring sweat rate of a subject using a wearable system. A sweat rate may be determined automatically based on one or more signals produced by a wetting sensor module in response to a presence of sweat in the wearable system. The one or more signals may be produced using a sweat presence monitoring device, for example comprising two or more electrodes that are operable to make conductance measurements. In some embodiments, sweat drops are periodically collected by the wearable system and individually detected by the wetting sensor module such that the sweat rate is determined based on the periodic detection of the drops. In some embodiments, an energy barrier is used to produce periodic flow of sweat through the wearable device detected by the wetting sensor module such that the sweat rate is determined based on the periodic flow.