Recently, I've heard three urban myths about the human body and I'm going to take the next few days to debunk them rather quickly.
Question: Your Body is 90% Water. True or False?
Answer: False!
Although I do have a background in biology, this is not needed to quickly think through this idea, especially if you ever have seen a human skeleton. Consider your bones. The human body contains many bones, some of them fairly large. The entire volume and weight of the human skeleton is much higher than 10% of the body. Additionally, every cell is has thousands of different carbon-based molecules such as proteins, lipids, nucleic acids, each performing a different function in parallel. Animals eat food for both energy and raw organic materials. If our bodies were only 10% carbon-based, then we would consume much less solid food at dinner and instead would be drinking more fluids to maintain that 9:1 ratio.
Yet, the human body does contain a very significant amount of H2O as it is about 60% water. What is true is that one should drink, on average, 2 liters (approximately 8 glasses) of water each day to re-hydrate due to a variety of biological functions. You can read the more detailed health recommendations on this topic from the Mayo Clinic here.