I did drain it almost entirely in October, I think and then refilled it. I'll do a 70% or so swap just to be safe.
Well water or city? You have to be careful of chloramines in any water change with municipal water, highly toxic. And temperate changes shouldn't be too quick. Better to do a 40-50% change one day, then another one in a day or so than all at once. If you have the time, of course.