Why are diamonds insoluble in water?

Answer 1

Diamonds are pure carbons held together through covalent bonding and forming a giant structure, there is no net charge on diamond so not attracted by polar water molecules and can not dissolved by water.

Answer 2

Diamonds are insoluble in water because of their strong covalent bonds. These bonds make diamonds highly resistant to chemical reactions, including with water. Additionally, the structure of diamonds is tightly packed, which further prevents water molecules from penetrating and breaking down the bonds.