If you heat water (steam) past a certain temperature, will it "glow"?

[Squink]

You need to get water considerably hotter than ‘red hot’ to make it decompose into hydrogen and oxygen:

At high temperatures, above about 1800 K, water vapor (steam) begins to dissociate into a mixture of H2, O2, H2O, O, H and OH. The extent of dissociation increases with increasing temperature and decreasing pressure. The water and the diatomic hydrogen and oxygen species completely dissociate into H(atomic hydrogen) and O (atomic oxygen) above about 3500 K under equilibrium conditions at 1 mm Hg absolute pressure.

http://www.hionsolar.com/n-hion96.htm

So you should be able to heat water to about the same color temperature as an incandescent light bulb, 2700-3300°K, before it starts dissociating.
Now some materials are better at emitting blackbody-like radiation than others*, but I don’t think any, including water, are so unemissive as to not glow visibly when you heat them to 3300°K (5500°F).

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*see Thermal emissivity