While water boils at 312 degrees. 
 This is only true if you live 43 miles below sea level.   <img src="/images/graemlins/grin.gif" alt="" />
I've been drinking one to two liters of water every day out of the same Nalgene water bottle at work for well over a decade.  I don't know what it's made of (not Lexan).  It's translucent white in color and softer than Lexan.  I'm not dead yet.
I imagine companies who make water bottles test them for toxicity.  If they fail, they'd make them out of some other material.  I really doubt Nalgene wants a bunch of dead customers laying around causing bad PR, just so they can use Lexan.