(No, it doesn't have to be 'nalgene'.)
Ages ago I posted a crochet cozy for my chilly, cumbersome waterbottle in the crochet forum.http://www.craftster.org/forum/index.php?topic=24597.0
Now I have a knit version.Ta Da!!
It's felted in briggs and little. More info at my blog: http://pomoboho.blogspot.com
Leave me a comment if you're interested in the pattern (it has some crocheting components to make it sturdier) I'm selling some with intarsia motifs...skulls, "H2O"-ha ha so clever!, flowers and lightning bolts -any more ideas welcome!