small pond over water line - freezing issues?

I have a 1/4 acre urban plot and started digging a small garden pond last year.  Its probably only a foot and a half to two feet deep.  I just figured out that our water service line may be running where I began to dig.  We had a mild winter here, so nothing froze but I'm concerned about having lowered the frost line.  Just wondering if when I fill the pond with water if the water will act as an insulator like the soil had or if I should just move the whole thing somewhere else.

In my area they put water supply lines even deeper than the normal frost depth.  I've always assumed that is to account for any landscaping that may change the ground level.  My guess is that you'd be fine..  

You could always call your city water people and ask them.