Regulation of Water Balance
University of Hawai‘i at Mānoa Food Science and Human Nutrition Program and Human Nutrition Program
As you eat a bite of food, the salivary glands secrete saliva. As the food enters your stomach, gastric juice is secreted. As it enters the small intestine, is secreted. Each of these fluids contains a great deal of . How is that water replaced in these organs? What happens to the water now in the intestines? In a day, there is an exchange of about 10 liters of water among the body’s organs. The osmoregulation of this exchange involves complex communication between the brain, kidneys, and . A homeostatic goal for a cell, a tissue, an organ, and an entire organism is to balance water output with water input.
Regulation of Daily Water Input
Total water output per day averages 2.5 liters. This must be balanced with water input. Our tissues produce around 300 milliliters of water per day through metabolic processes. The remainder of water output must be balanced by drinking fluids and eating solid foods. The average fluid consumption per day is 1.5 liters, and water gained from solid foods approximates 700 milliliters.
Figure 3.5 Daily Fluid Loss and Gain
Dietary Recommendations
The Food and Nutrition Board of the Institute of Medicine (IOM) has set the Adequate Intake () for water for adult males at 3.7 liters (15.6 cups) and at 2.7 liters (11 cups) for adult females.[1] These intakes are higher than the average intake of 2.2 liters. It is important to note that the AI for water includes water from all dietary sources; that is, water coming from food as well as beverages. People are not expected to consume 15.6 or 11 cups of pure water per day. In America, approximately 20 percent of dietary water comes from solid foods. See Table 3.1 “Water Content in Foods” for the range of water contents for selected food items. Beverages includes water, tea, coffee, sodas, and juices.
Table 3.1 Water Content in Foods
| Percentage | Food Item |
| 90–99 | Nonfat milk, cantaloupe, strawberries, watermelon, lettuce, cabbage, celery, spinach, squash |
| 80–89 | Fruit juice, yogurt, apples, grapes, oranges, carrots, broccoli, pears, pineapple |
| 70–79 | Bananas, avocados, cottage cheese, ricotta cheese, baked potato, shrimp |
| 60–69 | Pasta, legumes, salmon, chicken breast |
| 50–59 | Ground beef, hot dogs, steak, feta cheese |
| 40–49 | Pizza |
| 30–39 | Cheddar cheese, bagels, bread |
| 20–29 | Pepperoni, cake, biscuits |
| 10–19 | Butter, margarine, raisins |
| 1–9 | Walnuts, dry-roasted peanuts, crackers, cereals, pretzels, peanut butter |
| 0 | Oils, sugars |
Source: National Nutrient Database for Standard Reference, Release 23. US Department of Agriculture, Agricultural Research Service. http://www.ars.usda.gov/ba/bhnrc/ndl. Updated 2010. Accessed September 2017.
There is some debate over the amount of water required to maintain health because there is no consistent scientific evidence proving that drinking a particular amount of wate