Vacuum Level Required to Boil Water

At sea level, water begins to boil and change into a vapor state at 212 degrees Fahrenheit. If we increases the pressure we can raise the boiling point of water. If we wish to lower the boiling point of liquid, we simply remove the pressure that's on top of that liquid. That's how we boil water out of an air conditioning system. We use a vacuum pump to bring the system to a level of near perfect vacuum so the water will boil off and be carried away as a vapor. It's important to note that ambient temperature has much to do with the point at which liquids will boil under vacuum. The greater the temperature, the fewer microns of vacuum will be required to start the boiling process.

The chart below shows how temperature plays a role in the level of vacuum needed to boil water. 

All values are at sea level.  Subtract 1 inch for each 1000 ft. above sea level