[ARCHIVE ANSWER]
Yes. My K-9 has alerted on numerous toilets leading me to stashes hidden underwater inside the tank. We know through later tests these were not "residual alerts" but the odor traveling through water. I am not one to be crude but it was explained to me like this, "Ever fart in a bathtub?"Also, the more moisture in the atmosphere, the stronger any scent comes across. (Think about how a wet dog smells to us humans.) The moisture in nasal passages magnifies scent. So scent carried on water vapor would reek to a K-9.