26. Health Myth: You should drink exactly eight glasses of water a day.
People think everyone should drink a solid eight glasses. Commonly referred to as the 8×8 rule, eight 8oz cups of water a day are about two liters of water a day. What is frequently left out of this equation is that your water intake will also include the foods you are eating. So, if you are eating primarily whole foods, this will also increase your water intake. However, drinking two liters of water a day is not enough for more people, even though it sounds like a lot.
That is why this is used as a baseline, more to just get people started. Our bodies are made up of mostly water, around 67%. To calculate how much water you should be drinking, take your total body weight and multiply that by 67%(or 0.67). If you are 150lbs, you will take 150×0.67, which equals 100.5. We can round our numbers to make this easier to remember. Someone who is 150lbs should be drinking 100 ounces of water per day (or 12.5 cups, or 2.96 liters). If you exercise regularly, you will need to up your water intake, about 12 ounces for every 30 minutes you work out.