The water temperature here can vary anywhere from the mid 60's to the mid 80's Fahrenheit, 18-29 C, depending on the time of year and depth. Many times in the summer on shallow dives I will wear shorts and a rash guard but on most of my dives I wear a 3mm as I can always flush a little water in if I am too warm. If it is really cold I will add a hood or hooded vest and that makes a huge difference.