If someone asked what the most important molecule in your body is, most of us would say water. It makes up about 2/3 of our body weight! That is why a wrestler trying to “make weight” for a match can drop several pounds simply by sweating off water (not a good idea by the way). Whenever there is speculation of life on other planets, the question always arises: Is there water on the planet? What is so special about water? What makes it essential for life? Wouldn’t some other fluid work as well? These are some of the questions that we will attempt to answer in this unit.