The last few weeks I have tried cold showers, I would guess around 70 deg. Now the first few times was sort of chilling cold, but after a few tries it's not really that bad.
I start by washing my hair, then one arm, another arm, then one leg, then another and last the main body. It's really only the first minute thats sorta cold , after a while it's not too bad

Now I'm not saying ice water from Lake Michigan at 28F....sucked from under the ice, but maybe water from your tank ?
Any others ever try this ? If I get a chance I'll try to measure the exact water temp and report back.