Scanning electrochemical microscopy (SECM) is used to detect and observe the presence of water inside polymeric film at the microscopic scale around 200–500 μm. The principle is based on the use of SECM performed with a room temperature ionic liquid (RTIL) and K4Fe(CN)6 as redox sensor. The particular electrochemical behaviors obtained in such medium have been investigated by performing cyclic voltammetry and approach curves in negative feedback mode. Then, the cross-section of epoxy resin films has been repeatedly scanned using the SECM probe over several days of immersion in the RTIL. As the presence of water impacts the electrolyte viscosity, the electrochemical signal was sensitive to the amount of water around the microelectrode. The sensitivity of this technique to the presence of water released from the materials at the microscopic scale was demonstrated by comparing electrochemical signals obtained on dry and saturated specimens. Such results appeared to be very promising for the development of new methods to locally detect the presence of water in thick polymeric materials and to measure humidity gradient within the material thickness.