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Assuming you have container with heat insulation (something like boiler).
You can store water at any temperature below 100°C. At these conditions, you can drill a hole into container and store water at air pressure.
But when you heat water to tempertature over 100°C, it starts to boil, increasing pressure in contailner. If you drill a hole, water will start to evaporate and that'll cause temperature drop. If you try to maintain constant temperature, after some time all water will evaporate.
Water with temperature over 100°C can be stored only at high pressure?
If so, it'll reach some pressure (depending on temperature) and stop boiling?
Are there any other risks besides high pressure to be aware when trying to store water at these conditions?

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At high enough pressure you can keep water as a liquid above 100°C. With even more pressure you can even keep ice above 100°C. Similarly you can boil water at room temperature with a low pressure.

https://en.wikipedia.org/wiki/Phase_diagram (https://en.wikipedia.org/wiki/Phase_diagram)

The phase diagram of water shows what state it is in at any given temperature and pressure.

edit: To answer Phil's question. The very steep vertical line between the blue(solid) and liquid(green) at 0°C shows why pressure isn't the reason ice skates have a film of water to slide on. You would need to increase the pressure to a few kbar to get liquid at even slightly below freezing. See how far vertically you would need to go to hit the green area starting to the left of the vertical line at 0°C

It is actually the friction between the blade and the ice that creates heat which melts the surface.

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  • $\begingroup$ The interesting bit about this diagram is of course the green peak to the left, at -22°C and 209.9 Mpa. That's really cold liquid water. $\endgroup$ – MSalters May 9 '14 at 12:01
  • $\begingroup$ Is that the place under your ice skate's blade? I was taught long ago that you can skate/glide on ice because the pressure melts a little bit of ice. Is that still the accepted explanation? $\endgroup$ – Phil Perry May 9 '14 at 13:33
  • $\begingroup$ @PhilPerry - added a longer explanation $\endgroup$ – Martin Beckett May 9 '14 at 14:00
  • $\begingroup$ Additionally, if you dissolve a salt in your water, you can greatly increase the effective area of the liquid part of the diagram. $\endgroup$ – Jesan Fafon May 9 '14 at 14:25

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