HOW MUCH WATER SHOULD YOU DRINK A DAY?

1. How do you determine if you are hydrated?Urine color is the easiest way to assess your hydration level. Ideally your urine should be very close to clear in color. As the color of your urine gets darker to hydration level is decreasing.

2. What happens if you are consistently under hydrated? Some conditions that are associated with mild to severe dehydration are the following: 

Urinary tract Infections, gallstones, constipation, hypertension, bladder and colon cancer, venous thromboembolism, cerebral infarcts, dental diseases, kidney stones, mitral valve prolapse, glaucoma, and diabetic ketoacidosis. 
Manz F. Hydration and disease. J Am Coll Nutr 26: 535s–541s, 2007.

3.  How do you get water? Your body’s hydration level is affected by water from food, pure water, tea, coffee and sodas.

Heller et al. found that up to 25% of the water you ingest comes from food.  However, food has a variable amount of water. For instance, some fruits are > 50% water versus  cookies being < 20% water. 

Heller KE, Sohn W, Burt BA, and Eklund SA. Water consumption in the United States in 1995–1996 and implications for water fluoridation policy. J Public Health Dent 59: 3–11, 1999. 

4. How do you lose water? You lose water through breathing, urination, and sweating. 

5. What is the standard suggestion for daily water intake? The standard answer I was always told from my primary care doctors was 8 (8oz) cups of water equalling 64 oz a day. 

Then when I entered the fitness world it was commonly suggested to drink 1 oz of water for half your body weight in pounds.  

Example: A 130 pound person would drink 65 oz of water a day. 

This suggestion seems to come from a book called How to eat, move and be healthy. 

The Institute of Medicine came up with adequate intake (AI) for people 18 – 70 years old or older. They suggest your combined water consumption from food, pure water and other drinks should equal  2.7 liters (91 oz) for women and 3.7 liters (125 ounces)for men. They found that many variables affect hydration including food consumption, water and liquid consumption, environment, and activity levels. This variability made a  definitive water recommendation hard. They suggest allow thirst be your guide to how much water you consume. 

These numbers are before exercise.

Institute of Medicine and Food and Nutrition Board. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride and Sulfate. Washington DC: National Academies Press, 2004. 

6. How does exercise affect water consumption? While exercising  the American College of Sports Medicine and the National Athletic Trainers Association suggest drinking fluids 5 – 11 oz for every 15 – 20 minutes of exercise. 
If you are exercising for exercising for 75 minutes or less then water is all that is necessary to rehydrate electrolytes. If you are exercising for longer than 75 minutes then use of sports drinks or carbohydrate + protein drinks can be considered. 

7.  How does caffeine affect hydration? I have heard from several sources that you should drink 8 oz of water for every 8oz of coffee to help replace the water loss. However, I have not been able to find any source to back up that suggestion. 

Based on a clinical trials review by Armstrong, caffeine intake between 100 and 680 mg ( 1 oz cup – 7 oz cups) has the same effect as water on hydration. Millard-stafford et al. found a similar finding stating that caffeine and carbohydrate solution had no negative impact relative to hydration, sweat rate, electrolytes, and other related markers.
Many of the sources writing on the topic of caffeine and hydration did not site peer reviewed journals for their sources. Then the journals I could find that researched this topic  only looked at athletic college age people over a short period of time. I could not find any information on the specific effect of long term use of coffee or soda on hydration. 

Therefore, my takeaway is that I would assess my urine color frequently to address my overall hydration level. Then I would trade a non pure water drink for a pure water drink as needed to achieve optimal hydration levels. 
Armstrong LE. Caffeine, body fluid-electrolyte balance, and exercise performance. Int J Sport Nutr Exerc Metab 12: 189-206, 2002.

Millard-Stafford ML, Cureton KJ, Wingo JE, Trilk J, Warren GL, and Buyckx M. Hydration during exercise in warm, humid conditions: Effect of a caffeinated sports drink. Int J Sport Nutr Exerc Metab 17: 163-177, 2007.