What causes your mucus to be thin clear and watery?

Hydration: Great that your mucus is thin, clear, watery! You are probably sufficiently hydrated. Most of the time, this sort of mucus is caused by allergies, but can be due to a cold or other infection too, if you are not dehydrated. In very rare cases, usually after head trauma, clear discharge may be from CNS fluid (fluid around the brain).

Mucus: Mucus changes depending on your hydration status. When dehydrated, mucus can be thick and sticky. When hydrated mucus is typically thin and watery. It is vital to stay hydrated as infections are more easily avoided when mucus is thin and watery.