One of the more well-known trends is the #gallonofwateraday encouraging participants to drink one gallon, or 4.5 liters, of water per day. But how much water do we actually need to drink daily?

That info is handy for simple culinary tasks. Say you want to make a gallon of iced tea. Do you know how many cups it can make without looking at the package? To add more complexity, answering ...