In reply to jonnyjaffacake: Hmm, that's kind of what I thought (my old Nalgene bottle, which seems to be made of similar materials, doesn't have one). I suspect it's either the bite valve or the cap itself which is leaking - I don't think the straw could be causing a leak. A pack of replacement bite valves costs almost as much as a new Eddy, so I'll definitely look at the warranty route first. The thing is only about a year old!