Dehydration paradox

Experts are beginning to disseminate an idea that seems radical, but could save lives: drinking large amounts of water on airplanes could increase blood viscosity (and increase the likelihood of a clot forming). In other words, drinking lots of plain water on planes can increase dehydration and make the blood thicker, stickier, and more likely to clot.

Why? It's not entirely clear, but cabin pressure and low oxygen content of airplane air may cause dehydration to be more acute. What the research does show, though, is that drinking plain water can actually be worse than not drinking at all, since it causes more frequent urination and leads to more dehydration.

The experts leading the efforts to disseminate this information point out that sports drinks that contain electrolytes are a good solution.

To simplify traveling with enough for one 8-ounce glass per hour, sports drinks are available in powdered form. Just don't use the airplane tank water! Be sure to mix the powder into bottled water (thankfully usually available on planes these days).

More info on this:

Hydration Info from AirHealth.org
Summary of Travel Thrombosis Info from Your Health Base