Chickenthief they said saliva not water. Teeth, microbes, chemical reactions and tongue strength can detach small portions of the substance you put in your face hole or directly transfer electrons depending on the difference of potential for electrical current of everything involved and even if it does not touch your taste buds you can still feel it. That is because the information of taste is sensed by the interference that the substance cause in the bioelectric stand by state of the taste buds. (electrolysis, static, impedance, ROE etc...)
Try placing spices, fats or sugars in sealed plastic bags and your tongue will still "feel" some difference between those.