I’m no chemist, but it’s likely just deionized water. It can irritate your mouth and throat since the ion-dipole force in water makes it electrostatically attra

I’m no chemist, but it’s likely just deionized water. It can irritate your mouth and throat since the ion-dipole force in water makes it electrostatically attract ions, and can likely pull them from the cells on the surface of your mouth/throat. I don’t fully know if that’s the reason it would burn because I don’t remember how strong these forces actually are, but if I remember correctly it’s dependent on the ion and the difference in charge.