Water can boil and freeze at the same time

At the triple point — 0.01 °C and a pressure of 611 pascals — ice, liquid water, and vapour coexist. Change the volume and the liquid boils and freezes together.

A pure substance has a triple point where three phases sit in equilibrium. For water, on the scale used for decades, that point was defined as exactly 273.16 kelvin, which is 0.01 °C, at a pressure of 611.657 pascals, about a sixth of a percent of atmospheric pressure. In a sealed cell, pump the vapour away and the liquid boils. Boiling takes heat. The remaining water freezes. All three phases are present and stable.

The kelvin has since been redefined through the Boltzmann constant. The triple point did not move. It is a fact about water, not a clause in a standards document. It is also nothing like a kitchen. At sea-level pressure the boiling point is 100 °C and the freezing point is 0 °C, and they do not meet.