The balanced molecular equation for the reaction between calcium and water is:

Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)

The complete ionic equation is:

Ca(s) + 2H2O(l) → Ca2+(aq) + 2OH-(aq) + H2(g)

The net ionic equation, which only includes the species that participate in the chemical change, is:

Ca(s) + 2H2O(l) → Ca2+(aq) + 2OH-(aq)