I just received an email from my mother-in-law, with a link to an article on Dr. Mercola's site. It seems that Nalgene bottles are being taken off the shelf because they contain BPA (bisphenol A), a toxic chemical that causes hormone disruption.
This article explains it all very well.
I'm sad to hear this because I had originally started using Nalgenes for their convenience, so that I could bring water with me without the cost and waste of individual plastic water bottles (which also leach chemicals into the water). I am now on the lookout for some type of water bottle that is safe- most likely I will end up with something stainless steel. I will let you know when I find one. For now, I will probably use stainless steel coffee mugs, although these are not ideal because they cannot be put in a diaper bag they have to stay upright and can't just be tossed in a diaper bag.
If anyone knows of a good substitute for these kinds of bottles (especially ones that aren't ridiculously expensive), please leave a comment and let us know!