# What is the vapour pressure of water?

....${H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s {H}_{2} O \left(g\right)$
Now this is a function of temperature...and of course at $100$ ""^@C, ${P}_{{H}_{2} O} = 1 \cdot a t m$. At LOWER temperatures, this vapour pressure is often referred to as the $\text{saturated vapour pressure}$...and it must be included for gases collected over water.