# Would water occur as a gas on the moon, because there is a vacuum?

In any case, I think you have the right idea. A liquid $\text{boils}$ when its vapour pressure is equal to the ambient pressure, and bubbles of vapour form directly in the liquid. The $\text{normal boiling point}$ is specified when the ambient pressure (and thus also the vapour pressure of the liquid) is $\text{1 atmosphere}$ (of course now we're down here on Earth).
At $100$ ""^@C, water has a vapour pressure of $1 \cdot a t m$. The temperature of the moon varies between $- 150$ ""^@C, and over $100$ ""^@C. However, the ambient pressure is much, much lower than on Earth. Even on the dark side of the moon, water is likely to exist as vapour (even ice has a vapour pressure). This site estimates that the pressure on the moon is $3 \times {10}^{-} 15$ $a t m$. Lunar water is thus likely to exist in the gaseous phase.