Try using targetexact instead of normal /target along with a clear target and a harm/exists statement on the cast. That way when you attempt to cast Bind Elemental you will always have an elemental targetted or nothing. Also you don't need to specify the spell in the #showtooltip line.
Code:
#showtooltip
/cleartarget
/targetexact Water elemental
/targetexact Elemental de agua
/cast [@target, harm, nodead] Bind Elemental
/targetlasttarget
The only flaw I see with this is targetlasttarget targetting an elemental if there are two around and you target both during the macro. You could solve this with a little focus juggling I guess. Set your target to focus at the start of the macro, then re-target your focus and clear focus at the end.