Yes, but two of the hydrogens/electrons ripped from water in the process of photosynthesis effectively reduce one of the oxygens from the CO2, regenerating one water: 2 H2O + CO2 -> O2 + CH2O + H2O (multiply atom numbers by various numbers to get the actual biomolecules that comes out the other side of the various carbon fixation pathways). Still needed since the oxygen production all happens from the photosystems splitting water rather than from splitting CO2, the photosystems never touch the carbon directly. That water is produced no matter what you're using as your electron donor.