Edema in Hands/Forearms

No matter how I choose to hydrate--and, right now, up to 2.5 hours, it is with water only, appoximately 6 oz. every 15-20 minutes (any less, and I will get very thirsty)--at about 1 hour, my hands/forearms begin to swell. Then, the longer that I run, the worse it gets, and it doesn't subside until a couple of hours after my run.

What does this indicate? Is it dangerous? What can be done to prevent/minimize it?

Any thoughts are most welcome...

I'm thinking you are getting hyponatremic....low sodium. The more water you drink, the more you dilute the sodium levels in your blood, so it tends to get worse as you go on. Try drinking a sport drink before you run or take some sodium tablets, eat a salty breakfast before you go out, something like that. Carry some salt tabs with you too, or even little packets of table salt.

Can you also get sodium from goo packets?

the vanilla GUs I have say they've got about 55mg of sodium per pack. or about 2% of your average daily allowance. might not be sufficient for those running and sweating a lot. but I've had some GI problems trying GU and electrolyte drinks at the same time. I'm going to try some type of GU2O, Heed or Cytomax next, which have some carbos as well as electrolytes.
I get the same swelling on long exertions (4-5 hrs of hike/running) drinking only water, but haven't noted it on shorter running only training. i probably eat/drink differently for those than for long h/rs.

I'm thinking along the same lines -- try electrolyte caps. I just posted to your previous topic (on hydration/fueling) regarding this. It may or may not help the swelling, but I'm a big believer in electrolyte capsules, or as suntrail says, even salt tabs or table salt. GU and sports drinks don't have enough sodium for serious replacement. One good thing about commercial capsules (at least, the Hammer product) is that they contain other ingredients you need when exercising, not just sodium.