With seeds (nucleation sites) and T < 4 °C:
Water quickly forms an ordered hexagonal-like ice network (hydrogen-bond lattice).
Without seeds:
Water can remain liquid-like even at negative temperatures (supercooled water).
It may freeze suddenly if a seed is introduced or the system is disturbed.
Why supercooling matters:
Freezing needs a starting “template” (a seed). If water is very clean and undisturbed,
it can stay liquid below 0 °C. Add a seed and the crystal network forms rapidly.
In nature, supercooled droplets in clouds can freeze instantly when they hit dust, ice, or surfaces
(important for weather and aircraft icing).