We did an experiment in university where we cooled distilled water, which was completely still. We managed to get the temperature down to -7C I think before it froze. It quickly rose to 0C when it started freezing. kinda cool.

I’ve seen youtubers repeat the experiment, think it’s called supercooling. It also causes longer time to freezing, and was one of many theories for the Mpemba effect

I heard hot water freeze faster when thrown in freezing cold air, because it evaporates faster - making smaller droplets and increasing the surface area