For some people a cold shower helps them to sleep better while for others it's a warm or hot shower that helps them to sleep.
For me personally it's a cold shower about an hour before bed that helps me to sleep.
Well I don't have the shower on straight cold water but more like lukewarm I just can't take the cold water hitting my body so I have to have a little hot water added into the cold water shower.
The cool water or warm water from the shower for some reason helps to trigger the sleep signals in your body and I find that I do sleep better and get much deeper sleep and feel more refreshed in the morning when taking a cool shower.