I seriously doubt that anything will penetrate or leak thru the plastic bottles themselves. I would guess any oxygen penetration is from ill fitting bungs or airlocks. I use the plastic water bottles just as much as I use glass and suffer no ill effects. Reminds me of an old joke about penetrating oil. A salesman came in and said this is the best penetrating oil ever it will penetrate anything. The mechanic say's,,,,,, If it is so damn good how the hell do you keep it in the can??