Are they water proof?

Yes, absolutely! They are totally, rubber/plastic, etc. except for the removable footbed which is covered cork and can be removed to let them throughly dry if they get all wet. My husband has worn out dozens of pairs of these through many, many years and loves them. He has had others and still goes back to these original Birkenstocks. He wears them whenever he is doing yard work, washing the car, anything outdoors! A bit expensive but they do last a long, long time. You can certainly were them "under" water if the situation arises.

Are these real Birki's they say made in China?

real birkis made in germany , made in china is a fake

Is the 7-7.5 women's actually the European size 38?

Yes it is; but with this particular style I actually needed to go down one size because they are fairly wide. Even after sizing down I added a sole insert. This helps them to stay on my feet especially when walking up stairs. I do love my super birkis though. I am on my feet all day at work and they are very comfortable.

do these have replaceable footbed

yes they do. But that takes away from the room you have in the shoe, so if you are looking to order them, order a half size bigger or they will be too tight... especially with socks on.