Yeah, I see that it says not for liquid on the website. I got mine years ago at a moosejaw retail shop, on the staff's recommendation about a wide-mouth container for peanut butter. Maybe it would work fine with industrial homogenized peanutbutter, but putting any sort of natural stuff in it results in peanut oil all over your pack. I started trying to use sun-dried tomatoes in it a couple years later, when I'd forgotten about the earlier peanut experiences.
And to clarify: the nalgene bottle I linked to *does* leak, so I've replaced it with a "disposable" bottle that came full of juice, which seals fine.