I hope you didn't do what I did. Last fall I told Bill, "I need to put heat cables around the water pipes in Greenhouse". Promptly forgot about it. Actually it had never gotten below freezing in there. The little heater I keep in there has always kept it above freezing.
Who would have thought we would have sub-zero tempts in Middle Tennessee - for 3 nights straight! Needless to say I had a frozen water pipe at the back of my greenhouse. Our plumber (thank God, he is my neighbor too) just left from replacing that pipe and of course there is no heat cable to be had within 50 miles of here. Good ole Amazon Prime to the rescue! I found and ordered this cable and it will be here Saturday! No freezing weather predicted till then so I should be OK. I ordered the cable long enough to go ahead and wrap all the pipes in the greenhouse - even the ones that didn't freeze.
Another thing I did that didn't help any was put my big container of potting mix against that back wall and I'm sure it blocked some of the heat from reaching those pipes. I have a bigger heater now, no major damage done. Thank Goodness I was not sprouting tomatoes yet!
So learn from my mistake, install heat cables on your exposed water lines and heat your greenhouse if you plan to use it in the winter!