I just put in a 9x12 greenhouse. Water is plumbed directly inside with a
dual carbon filtration system. I usually water with a spray wand, but it
seems like the ground water temps in January are going to be too cold to be
practical. How does everyone deal with water temps during the winter?

I am using two 55 gallon plastic barrels as a solar heat sink. I am thinking
about using one of these as my source for plant water, and would just refill
with ground water. Thoughts?