I'm in Europe. I've been using only (cold) tap water in my house for more than a year. It began with a broken heater in the midst of last year's summer when I decided to postpone buying new one to see how long I can last with cold water. I thought that sooner or later I should catch cold and then I would switch back to using warm water. That summer was hot (up to 35 degree Celsius) and tap water was warm, slowly it began cooling but I didn't feel any difference. When it hit -25 degree outside I was sure that my cold water showers will put me in bed but that never happened. The only inconvenience was (and is) that many hygiene products (shampoos, soaps, and such) work poorly with cold water and it takes more time to properly wash myself. I can't say whether this habit affects my weight or gives any other benefit, but as long as it's not harmful I can't care less.