The (X) over tilde (3)Sigma(g)(-), (a) over tilde (1)Delta(g), and (b) over tilde (1)Sigma(g)(+) states of the water dication, H2O2+, have been investigated using several high-level ab initio methods and a range of basis sets. With Dunning's augmented correlation consistent polarized valence quadruple-zeta (aug-cc-pVQZ) basis set at the complete active space self-consistent field second-order configuration interaction (CAS-SOCI) level, it is confirmed that the ground and first two excited states of H2O2+ are all of D-infinity h symmetry, in violation of Walsh's rules for 6 valence electron AH(2) systems. The singlet-triplet splitting ((X) over tilde (3)Sigma(g)(-) -- (a) over tilde (1)Delta(g)) is predicted to be 53.6 kcal/mol (2.32 eV, 18 700 cm(-1)), while the (X) over tilde (3)Sigma(g)(-) - (b) over tilde (1)Sigma(g)(+) separation is predicted to be 91.1 kcal/mol (3.95 eV, 31 900 cm(-1)). The vertical double ionization potentials (IPs) from (X) over tilde (1)A(1) H2O to the (X) over tilde B-3(1), 1 (1)A(1), (b) over tilde B-1(1), and 2 (1)A(1) states of H2O2+ are predicted within the cc-pVQZ basis to be 40.1, 41.2, 42.6, and 46.1 eV, respectively, in good agreement with recent double-charge-transfer spectroscopic results. The corresponding adiabatic double IPs are 37.0, 39.3, and 41.0 eV to the (X) over tilde (3)Sigma(g)(-), (a) over tilde (1)Delta(g), and (b) over tilde (1)Sigma(g)(+) states of H2O2+, respectively. The activation barrier to fragmentation of H2O2+ ((X) over tilde (3)Sigma(g)(-) H2O2+ --> (3)Sigma(-) OH+ + H+) at the cc-pVQZ CAS-SOCI level is predicted to be 2.1 kcal/mol (0.10 eV, 738 cm(-1)), and the reaction is exothermic by 126.4 kcal/mol (5.48 eV, 44 210 cm(-1)), providing a challenge for direct experimental detection of this elusive molecule.