I'm not sure a 20 degree shower really counts as a cold shower. That is a comfortable swimming temperature on most summer days and people can easily spend 20-30 minutes in water just to cool off even if they are unaccustomed to taking cold showers at home.

I've only been to such hot countries on vacation, and I think if asked, most people would confirm that they mostly don't use the hot water, except perhaps to sanitize hands with soap.