In my location "cold" water is pretty uncold this time of year. My thermometer is not very accurate but I was getting a reading in the high 60s Fahrenheit (near 20 C). I've been experimenting with keeping the shower stream hitting the back of my head and running down the back of my. I do that so that my breathing is not impeded. I suppose I could buy a facemask and a snorkel but I don't know if that is necessary.
I've always read that more heat is lost through the head. If so, it makes sense to do what I am doing during the summer months. This study
seems to support placing the back of my head under the shower head.