I'm reading about (standing) sound waves and one example is that of an vertical pipe that has a standing sound wave in it. It is then filled halfway with water and since the length of the pipe decreases, the required fundamental frequency increases.

Now what I don't understand is how the water just acts like the bottom of the tube. The standing wave should be caused by the reflection of the sound waves that are sent in, but don't the waves continue into the water?

I found a picture that illustrates a standing sound wave on top of the water, where the water surface works like a displacement node.

[![enter image description here](https://i.stack.imgur.com/KVHOj.png)](https://i.stack.imgur.com/KVHOj.png)