Why does water go from your mouth to your nose?

Direct link: There is a direct passageway between the back of the mouth & nose. Gravity & coordinated drinking habits sends fluid down the swallow tube. If circumstances permit, fluids can go backwards into the back of the nose & out. There is no valve or wall preventing this.

Nasopharynx: The back of your mouth is connected to your pharynx via the oropharynx. Liquids can sometimes move upwards through the nasopharynx into your nose due to backpressure.