# How is the boiling point of water altered at pressure LESS than 1*atm?

Well it is less than $100$ ""^@C.
The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid is equal to the ambient pressure, and bubbles of vapour form directly in the liquid. The normal boiling point is specified when the ambient pressure is $1 \cdot a t m$, and of course the vapour pressure of the liquid is also $1 \cdot a t m$.