# $\mathbb{Z}_2$ Symmetry in Water

I have learned that the critical exponents for phase transitions is independent of the microscopic structure of the substance and is dependent on the symmetry. For instance the phase transition for a ferromagnetic at the Curie temperature and the phase transition for water at the critical point have the same critical exponents. The ferromagnet has $$\mathbb{Z}_2$$ symmetry is related to spin up ground state and the spin down ground state. What will be the $$\mathbb{Z}_2$$ symmetry in water?