Well when you're dealing w temps in of -30...any amount of water anywhere freezes pretty much instantaneously.
So watering an arena in mid winter wouldn't be productive at all.
We installed all our heat trace tapes on our outside water lines by ourselves. As long as you have basic knowledge of electrical and plumbing...it isnt that hard. And it wouldn't work in winter anyway, as the moisture on the outside of the sprinkler head it self would freeze up, as there is no way to protect that from exposure....thats another reason why using it in winter wouldnt be ideal in cold temperatures.
I know 3 other barns that have sprinkler systems in thier arenas, and they have never had issues with them bursting or cracking from any water left in the lines.......and yes I know they don't drain them specifically or blow the lines out, as I asked.
We were thinking of adding a sprinkler system to our arena, but when I found out the cost, and the cost of having the calcium put down, I decided for the latter....
As w the calcium its a one shot deal, opposed to w water you'll be doing it several times a year.
We do it late fall....that way it has its best effect over winter (which yes makes the footing dry) and then we are good till the following fall.
We may have to water it once during the summer, but usually not as we ride outside in summer for the most part.
If it isn't built to drain they'll freeze solid and burst, something your more likely to see in climates where it doesn't freeze enough for people to think about it. Or when someone moves from warmer climates to colder and haven't learned lifes little lessons yet.