Really depends on where you're from I think. I live in Tampa and you couldn't pay me to go in the pool until the water temp is around 85ish lol. My parents live in NY and came to visit us in January and went swimming in our UNHEATED pool!! Even in the our coldest months, days that don't get above 60 are pretty rare. Nights can get cool, this past winter was very mild and a few, maybe 3 or 4 nights were 30's or 40's. I'd expect 70 degree weather in December or January, but you really never know.