Wdym? -5c isn't that cold, that's the usual setting for cold showers, isn't it? Idk how that measurement works. Average temperature here is like 10c on a good day. It's Baltic up north. The cold doesn't bother me much unless it's very, very cold like -7c+
There's some scientific research that concludes cold showers in the morning after waking up and hot showers just before bed change your body temperature to help you have more energy during the day and sleep more deeply at night.
I started to take cold showers after I do a lot of exercise and even at the coldest setting, it's tolerable. I'm slim so no extra insulation and I don't get shrinkage either in cold water, but that's actually a problem on its own for another thread to try to sort out solutions to live with that issue lol. Sometimes I do shiver a lot at the start.
