Do you get a headache right after, or much later? I bike, I don't run, so the slosh factor is less evident when I drink while I ride. But I use a camelpack and just sip along the way. I'll drink somewhere between 1 and 2 liters in an hour (on the high end lately because it's so stinkin' hot here). In the past I would come home and *maybe* finish up what was left in my pack and call it done. More recently, I've started drinking more throughout the day after I get home...maybe a glass an hour or so? This way I'm not building up so much at one time. I've never got the sloshy feeling (I mean, I've had it, so I know what you're talking about, but what I'm doing isn't enough to make me feel sloshy).

The water I take with me has the electrolyte powder in it. Lately I've also been adding a pinch of salt (because I am actually sweating and I can feel the salt on my skin; my powder has potassium and maybe magnesium, I'd have to check, but no salt). The water I drink when I get home is plain water.