Water is essential for life. It helps to regulate body temperature, keep joints lubricated, delivers nutrients to cells and keeps organs functioning properly. In fact, research demonstrates that even mild dehydration can impact cognition, mood and physical performance. Despite its importance, there is no Recommended Dietary Allowance (RDA) for water or fluid intake, making it difficult to know exactly how much water we should be drinking. Here are some facts about hydration, including the current Adequate Intake Guidelines, that will make it easier for you to meet your hydration needs.
Sources of Water
Plain drinking water is not the only source that contributes to our daily water requirements. What we eat, the beverages we drink and what our bodies produce collectively contribute to our overall water input.
Food
Typical U.S. diets contribute about 20% of daily water intake. When it comes to food, fruit and vegetables (and soup, of course) have the highest water content, with cantaloupe, strawberries, watermelon, lettuce, celery, cabbage and pickles coming in at the top of the list. Dairy foods (milk and cottage cheese) also have a relatively high water content. Foods low in water include nuts, crackers, bread and oils.
Beverages
Milk, coffee, tea, sports drinks and soda all contribute to daily water intake. However, it is important to be mindful of the quality of these beverages. Soft drinks do not provide nutrients nor satiety, and sports drinks often contain unnecessary added sugars. As such, it’s important to limit consumption of these beverages and rely more on water, coffee and tea to meet water needs. Lastly, while coffee and tea are commonly thought to be dehydrating, research does not support this belief. Coffee is a mild diuretic and may increase water output, but the caffeine content is not high enough to cause dehydration on its own.
Metabolism
Our bodies produce water during metabolism; however, the water produced contributes less than 10% of our daily needs (~1-1½ cups per day).
Water Requirements
Due to the precise mechanisms that regulate water balance, a wide range of fluid intakes generally meets hydration needs. However, individual water requirements vary based on age, gender, climate, physical activity and diet.
Age
As we age, fluid intake tends to decrease, so we must be increasingly mindful of remaining hydrated. Explanations for this trend include a fading sensitivity to thirst sensations, chronic diseases, and/or purposeful reductions in fluid intake in order to minimize the frequency of urination. Fluid output may also increase due to certain medications or an age-related decline in the kidney’s ability to concentrate urine.
Climate & Physical Activity
In hot climates or during physical activity, the body produces sweat as a mechanism to lower body temperature. The water lost through sweat should be replaced by increasing water intake under these conditions.
Adequate Intake
Despite the lack of an RDA for water, an Adequate Intake (AI) has been set to provide guidance for water intake. The Institute of Medicine recommends that men and women achieve a daily total water intake of 15 cups (3.7 L) and 11 cups (2.7 L), respectively. While this may seem like a lot, it is important to take food and other beverages into account. If you are following a healthy diet (one high in fruits and vegetables), food may contribute up to 35% of daily water needs. As such, the required intake of water drops to approximately 10 cups (2.4 L) and 7 cups (1.8 L) for men and women, respectively.
Summary
Water is a vital nutrient and has many important roles in the body. Despite the body’s precise regulation of water balance, we must still consume an adequate amount of water to prevent dehydration. While a specific RDA does not exist, it is recommended that men and women meet a total daily intake of 15 and 11 cups, respectively, including the water content in food and beverages other than water. Older adults and individuals in hot climates or undergoing intense physical activity should be mindful about increasing intakes to meet specific needs.