I'm not worried much about BPAs, for as often as I drink from them while hiking its still only while hiking that I consume water from a Nalgene. If TEOTWAWKI happens and I start drinking water fulltime from a Nalgene, BPA will be among the least of my concerns.

I'm a tad more concerned about present day water quality, things like the oil additive MTBE that has leached into the groundwater and are present in the everyday water supply of most of the US. I get that whether I drink from a Nalgene or not.