I've been practicing the Wim Hof Method of breathing and cold exposure for a couple of years now. We don't get temperatures as cold as Poland where one of the Wim Hof training centers is located, but I use what I have. The pool today felt colder than the air temperature which was 47º F, but I don't have a good thermometer for measuring low temperature water, so I am uncertain of its exact temperature.
This was the longest very cold water exposure I have had so far. I can't really describe how it feels to gradually gain control of some allegedly autonomic functions. The best word I have at the moment is EXHILERATING. As you will see in the video, after a session like this, I feel awesome and deeply grateful for Nature and my life.
At this moment, I am able to control my response to the cold for about 10-15 minutes. This seems to be getting longer the more I practice. It has not happened overnight. The period of time I can remain free of shivering has gradually increased over the period of time I have practiced.
Following Wim's advice, I don't push myself when I feel unprepared. Most days I take a long cold shower (as cold as I can get), but when I feel averse to it, I take a contrast shower or even a strictly hot shower. Sometimes I feel a need to do that for several days, then I return to the cold showers.
I've also recently started incorporating cold air exposure. I do the Wim Hof breathing method outside, and have been doing it with less clothing insulation when I feel the ability.
One note: In this video you will see me doing some deep breathing while in the water. This is not recommended. I have never felt faint when doing the breathing but some people do get faint and you don't want to faint in the water as you could drown.