Existing sensing technologies lack the ability to spatially resolve multiple sources of water or humidity without relying on the deployment of numerous inline sensors. A fully distributed approach has the potential to unlock a diverse range of applications, such as humidity mapping and liquid-depth measurements. We have explored a new direction toward what is, to the best of our knowledge, the first non-bending fully distributed water/humidity sensors. This new class of sensors was made possible from the first combination of small-core exposed-core fiber, a hydrophilic polyelectrolyte multilayer coating, and coherent optical frequency-domain reflectometry. Their non-bending nature enables deployment in a wider range of environments compared to the bending type based on water-induced fiber bending. The sensing mechanism involves monitoring back-reflected optical signals Manuscript