I don't know of any studies into HDPE (because I haven't bothered to do any research), but the difference between my lexan nalgene and my HDPE nalgene is the HDPE imparts a definite and reasonably unpleasent taste to the water while the lexan does not. Harmful or not, there must be a chemical or three leaching into the water from the HDPE. I can taste the difference, so the levels are detectable.