Milk jugs won't last. They are not designed to withstand freezing either.
2 liter bottles may last longer but are also not designed for long term storage.

Do yourself a favor and splurge on a Scepter Runt. 2.5 gallons. About $25 and worth every penny because you won't have to worry about it failing on you.

Designed for military use. Millions of them in use all over the world.
These things are thick and tough as nails.
The 5 gallon versions can be seen strapped to tanks and humvees.

Freezing won't be a problem as long as you leave room for expansion,ie:don't fill it all the way up to the brim.

Water is important. Don't skimp on the storage container.