This doesn’t have anything to do with gear but. . .

Last weekend I was out for my first winter overnight and it was great! The overnight low is a bit of a debate right now. Weather.com says it was only 19 degrees but I think it was around 1-3 degrees. My reasoning is that the following morning 1/16" of water would freeze solid in a cook pot in under three minutes.

Anyways my question is about storing water overnight. I placed water in two nalgene bottles (forgive me, light weight water storage to come!) and placed them upside down in a snow bank. I then covered the water with 2-3 feet of medium density snow on all sides. The next morning the water along the perimeter of the bottles was frozen about an 1/8 inch thick and the openings of the bottles where almost frozen closed!

What did I do wrong?