Coconut water with a bit of lime, and rum, medicinal use only, is okay but it's generally taken orally as a libation.

But what if you need IV fluids? According to this you can tap the coconuts:

Where I read about it recently:
http://www.straightdope.com/columns/read/2925/can-coconut-juice-be-used-as-blood-plasma-plus

An interesting PDF that gives detail information:
http://pinky.ratman.org/~drolley/PDF/inject%20some%20coconut.pdf

Mentioned in:
http://www.docstoc.com/docs/25580924/Discussion-of-IV-Fluids

There are other references in the professional literature but, unfortunately, you need the subscribe or but each paper individually. It gets pricey to casually explore a subject.

So what do everyone think? I don't think coconut water would be my first choice of IV fluid. I would lean toward the plastic bags with the fancy labels as long as they last. But given a lack of other options, and a patient that will surely die otherwise, I might give it a go. Not everyone will, or needs to, see it that way. Discuss.