Thank you Matt_Aufderheide. The transparency is working now.

But now, I found a bug. The objective of the transparency is to show a little of what is underneath of the water. Therefore I put a block underneath of the water, because before I didn't have anything there. Only that now it appears another reflection layer above the water.

In this pic, you can see the bug layer. It only appears in areas that have something under.


Here I am under that layer.


And here, I am above that layer.