[gundog]

Might work with sparkling water. Still heavy as hell, though.

[John Locke]

Not such a crazy idea. After all, 8/9 (81%) of the mass of water is due to the oxygen. And since oxygen gas muct be kept in pressurized tanks, while water can be kept in plastic bottles, you probably save on mass overall by taking along water instead of oxygen.

And yes, water must be kept liquid. But so must the crew - and a big tank of water would make an excellent heat buffer to smooth out variations in temperature.

Getting the bubbles out is easy - you need only a very small difference in weight, and you can do that with a turntable.

The big problem is the energy needed to split the water into H2 and O2, and yes, as has been pointed out, no way will there be enough energy in starlight.