Here's why:

* Ionic Bonding: Zirconium oxide has a very strong ionic bond between the zirconium and oxygen ions. This bond is very difficult to break by the polar water molecules.

* High Lattice Energy: Zirconium oxide has a high lattice energy, meaning the ions are tightly packed together in the crystal structure. This makes it resistant to dissolution.

While zirconium oxide is insoluble in water, it can be dissolved in strong acids like concentrated sulfuric acid or hydrofluoric acid. However, these reactions are highly corrosive and should be handled with extreme caution.