When I drink water during POIS, I get very bad chills. It makes it almost unbearable. Honestly, I feel a lot better, in POIS, to be just a little bit dehydrated. One thing I suggest, since most of us are taking Niacin, is to, when you drink lots of water, make sure to get enough salt as well. Vasodilators like Niacin can lower your blood pressure, causing worse brain fog, and lightheadedness when standing. Salt can help to raise your blood pressure a bit to a better level. I prefer pretzels.