I waited way too long to order this. Why? I wasn't sure it would fit in my narrow-mouth water bottles. It does. Not only does it fit through the opening (trust the images), but it's got some flexibility to it so you can swish it around and get the whole bottom of the bottle clean without a lot of extra effort. I also love the curved end that allows me to get up under the neck of the bottle where it is a little wider than the mouth. I don't think I've ever seen any other bottle brush with this feature. Wish I would have ordered it sooner!