I understand from a previous post that there is a Rabbinic gezera of bathing on Shabbat, which I assume holds also for a cold shower. If you tend to have oily hair and skin and not comfortable without a shower is it permissible to take a cold shower on Shabbat?
Thank you very much.
Yes
How cold does the water have to be?
There are two issues. One is turning on the hot water. That’s a problem no matter how much. I’m not addressing that point right now.
The other issue which is discussed above is regarding the Gezera of bathing. For that, a cold shower is allowed. Cold doesn’t have to be freezing. There’s no specific temp. I’ll point you to the Aruch Hashulchan 316:3 that says it’s not clear to him, but we go by what people consider hot. For example if people consider 100° F to be hot, it has to be less than that.
See also שש"כ י"ד י"א.