On a NIST (National Institute for Standards and Technology) page on the molecular details of water and it's various isotopologues, I came across this:
Electronic energy: -76.4089547246 hartree
There is, really, no other context on the page....
I found the page after typing in 'ionization energies of water'....
I put this here on Chemistry SE rather than Physics SE, I hope that is OK....
I DID look around to try to find an answer elsewhere, before coming here and posting...