Drinking sufficient water can support immunity, help with circulation, regulate body temperature and serve as an appetite suppressent — all worthy goals at the start of a new year. In rare cases, however, you can drink too much, causing nausea and headaches, and in extreme circumstances, vomiting and diarrhea. So what’s the magic number? How much water should we actually be drinking? It’s not an easy answer, and body weight, activity level and environmental factors...