Forget six to eight glasses of water a day. Although each pregnant woman’s optimal intake varies depending on body mass, in the summer, your best bet is to have a water bottle with you at all times. Plan on having at least one extra glass a day to account for what you sweat out in the heat, plus another for each episode of light activity. We’re especially dehydrated in the morning, so be sure to start out the day by drinking a tall glass of water. As your pregnancy goes on, it becomes more and more essential to drink plenty, since "dehydration is the number one cause of pre-term labor," says Ceridwen Morris, a certified childbirth educator and co-author of the pregnancy guide From the Hips: A Comprehensive, Open-Minded, Uncensored, Totally Honest Guide to Pregnancy, Birth, and Becoming a Parent. "Some people mistakenly think drinking water increases your water weight and leads to swelling,” Morris adds, “but the opposite is true: the more you drink, the more bad stuff you flush out."