needs a picture / proper structure
I do not believe using spaces between ladders should be considered a bug or an exploit as the character is two blocks tall thus can reach a ladder one block up which is realistic, and most likely intended.
They do block water
before placing the ladder
after placing the ladder
There was a good wait before I took the second screenshot after I placed the ladder to block the water so I'm pretty sure that they block water and this should be changed accordingly