Don't break any walls.

There is only one entrance to the library.

No draining the water from the entrance, as water is still pouring in.

With all of that, bring this large body of water outside.

Those are...

...the important rules.

A convenient method...

But why aren't there any other doors in the first place...?

Everyone could just swim underwater and get out, except for Remy.

I've got it!