how much pressure has to be on water for it not to freeze at 32 degrees?

Answer 1

Lowering the freezing point of water 1 degree C requires a pressure of 135 ATM ! Recall that one ATM is approximately 14 psi.
For all practical applications, applying pressure is not a very reasonable method of lowering the freezing point of water.

Answer 2

Water freezes at 32 degrees under normal atmospheric pressure. Increase or decrease the pressure, and the freezing point will change.

Answer 3

If you want to know the freezing point of H2O at any pressure, this calculator will tell you:

http://www.csgnetwork.com/h2ofreezecalc.html

Note: This is primarily for sea-water. For fresh water, just enter a "0" for "PSU." The pressure is gauge pressure. If you want absolute pressure, subtract 14.7 psi, or 101.3 KPa from the number you enter.

Answer 4

Don't hold me to this, but doesn't the freezing point also depend on purity. I think that freezing needs some impurity to nucleate around. To get "supercooled" water, it has to be very pure.

This phenomena can be observed by flying in rain or snow where the condensation is actually below 32F. It freezes on the flying surfaces because the surface introduces a material the condensation can nucleate around.

(Supercooled water refers to water that is colder than the freezing point and still liquid and fluid.)

Answer 5

I would imagine at least more than 1 atmostpheric pressure (our constant) at sea level.