Can the straps be adjusted?
There is one long strap that can be adjusted.
Is there aremovable strap?
Yes. The straps can be removed, but there is a hook and loop with the other end of the plastic buckle attached.
Is it resistant to water?
I am not sure but the material seems pretty sure.
Will it work for mac 13 inch?
It's too small.
Does this bag have an exterior pocket?
No, it has a closing zip.