However, a general guideline for the day of the event is to drink 16 to 20 ounces of water about 2 to 3 hours beforehand and then another 8 to 10 ounces 20 to 30 minutes before running, Kennihan says.

Take small sips . While it's important to stay hydrated, drinking large amounts of water at once can cause negative effects during a run. According to Dr. Justin Mullner, a sports medicine physician ...