How much water is too much?

In this heat, it's very important to drink lots of water, but there is such thing as drinking too much. It's called over hydration or hyponatremia, and it can make you very sick. Experts suggest men should drink 15.5 cups of water a day, while women should drink 11.5 cups. Symptoms of over hydration are headaches, vomiting, and nausea.