It's important to drink enough water year-round, but especially during the summer when you're sweating a lot of it out. But preventing dehydration - which can cause fatigue, nausea, muscle cramps, disorientation, fainting and shock - is more nuanced than that. Try drinking fluids with electrolytes rather than solely drinking water. It's also a good idea to rotate alcohol and caffiene out of your routine, if only every once in a while. Your goal is to drink at least half of your body weight in ouncles daily, and more if you're physically active.