Eight-by-Eight Rule from How Much Water Should You Be Drinking? (Slideshow)
How Much Water Should You Be Drinking? (Slideshow)
Your weight determines how much water you should be drinking daily. For example, someone who weighs 100 pounds doesn't need to drink as much water as someone who weighs 200 pounds. Keeping that in mind, your daily water requirement (in ounces) can be calculated by multiplying your weight by two-thirds.
Use this simple formula: Weight x 2/3 = Ounces of Water You Should Drink Daily
Replace What You Use
Considering the amount of water you lose when using the bathroom, breathing, and just living life, totaling about 2 to 3 liters a day, it’s necessary to drink more water to replace what you’ve lost.
Consider Your Activity Level
When you sweat, you lose water. You should add 12 ounces of water to your daily water intake for every 30 minutes of exercise.