How does the freezing temperature of water vary with respect to pressure?

I know when the pressure is reduced, the boiling temperature of water is reduced as well. But how does the pressure affect the freezing point of water?

In a low-pressure environment, is water's freezing temperature higher or lower than $0\sideset{^{\circ}}{}{\mathrm{C}} \, ?$

Answer

If you decrease the pressure, the freezing point of water will increase ever so slightly. From 0° C at 1 atm pressure it will increase up to 0.01° C at 0.006 atm. This is the tripple point of water. At pressures below this, water will never be liquid. It will change directly between solid and gas phase (sublimation). The temperature for this phase change, the sublimation point, will decrease as the pressure is further decreased. To learn more details, image google "water phase diagram" and study the pictures.