I have a waterbottle at work that has a screw on top, with a silicone nipple on a straw inside. When you bite the nipple, you can suck water out of it. The question is that the water remains very high up in the straw, Even if I squeeze the straw open to atmosphere, it only goes down a little bit, and never to the level of the water below. The straw is fairly wide, so this seems like more than capillary action. It seems that the air pressure inside the bottle is higher than ambient air pressure. But if anything, I'd expect it to be lower than ambient, since I'm drawing out water from inside (presumably there's some valve to allow air in so that I can drink from it at all).

What am I missing here?

Edit: NB: I may be a physicist, but I was never good with fluids. For some reason, we always skipped over that section in my classes.

Edit 2: I think /u/ked_man and /u/IAmNotABanana1 got a good explanation for this one. Water remaining in the straw starts to fall back down into the bottle, but since the air valve is now closed, the rising water it falls into compresses the air above, instead of just pushing it out of the way. This leads to the higher internal pressure than external pressure.