So, What is the Guideline for Water Again?

This question has been debated for quite some time, without a lot of definitive answers …until recently. So, we decided to provide a little refresher on how to stay hydrated even during the coldest winter months.

In February of 2005, the Institute of Medicine released the dietary report on water, salt and potassium. The panel came to some interesting conclusions about how much water (or actually fluid) a healthy, sedentary person needs on a daily basis. Using national data, it was determined that adequately hydrated women typically drink about 91oz. per day and men about 125oz. per day. These values represent total fluids, which include caffeinated beverages and the water contained in food. The report basically allows us to count all beverages, assuming caffeine and alcohol are consumed in moderation, and also says we should use thirst as the determinant for how much we need. Keep in mind; however, thirst is not the best indicator in extreme environmental conditions or for those who are very active.

Does this information mean that the old 8- 8oz. glasses of water are a thing of the past? The answer is possibly. To be honest, there really isn’t any scientific evidence supporting this recommendation, though it is still well accepted by many health organizations. Some experts actually think the recommendation came from a 1945 Food and Nutrition Board statement that was misinterpreted (1). In reality, some studies have shown that we need less than 8x8, while others have indicated more might be ideal. It seems like someone’s size, or more specifically body weight, may be an important factor.

The fluid guidelines determined by the Institute of Medicine are general recommendations, but how much do YOU need on a daily basis? Clearly a 120-pound woman doesn’t need as much fluid as a 250-pound man, assuming activity levels and environmental conditions are similar. One way to determine your fluid needs is to take your body weight (lbs) and divide it in half—then drink this amount of fluid ounces. This covers the typical losses from feces, urine, perspiration and respiration for your given body size. After that, activity level and environmental conditions may increase this number even further. Another way to calculate fluid needs is to drink 1 milliliter for every calorie you expend. This is the RDA for water and is based on the idea that water loss parallels energy metabolism (2). The RDA also included a recommendation of 1.5 milliliters per calorie expended, which would account for activity, sweating and solutes. I think the former guideline is more practical, being that it is very difficult for individuals to keep their calorie expenditure consistent from day-to-day.

Remember, staying properly hydrated is one of the most important things you can do for your health. Try to keep your urine looking somewhat clear or pale yellow and make sure your weight doesn’t fluctuate drastically from day to day. This will help ensure you’re getting the amount that you need. If you have any questions about fluids or hydration in general, talk to a registered dietitian.

Valtin, “Drink at Least Eight Glasses of Water a Day.” Really? Is There Scientific Evidence for “8x8”? 2002.
Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. 2004.