You probably never thought of water as a dangerous substance. It’s usually not. Every single cell in your body is made up of water. It makes up the majority of your blood volume and water even helps things move through your digestive tract. While you certainly need a lot of it to keep things running, it is possible to drink too much and make yourself sick.
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While no exact fluid recommendation exists, the Food and Nutrition Board of the Institute of Medicine has a general guideline for healthy adults. If you are male, aim for 3.7 liters daily, which is about 125 ounces. As a woman, your fluid recommendation is 2.7 liters a day, or around 91 ounces. This basic guideline includes water and all beverages, as well as food. You can actually get as much as 20 percent of your fluid recommendation from the foods you eat.
Maximum Safe Intake
You’ll need to drink more than the recommendation if you work out a lot, live in a hot climate, sweat a lot or live at a high altitude. Your kidneys excrete anywhere from 800 to 1,000 milliliters of fluid -- 27 to 34 ounces -- every hour at rest, explains Dr. Joseph G. Verbalis, the division chief and professor of medicine at Georgetown University. Thus, 27 to 34 ounces of water per hour should be the absolute most you can drink before you have a net gain in water, where cells become swollen with fluid and you retain water. This is when you might experience side effects. But your health status, gender, age and weight all have roles in how much water your body processes. You might be able to handle slightly more or slightly less.
Considerations for Athletes
While you’re exercising for extensive periods of time, like if you run marathons, your vasopressin level goes up. This anti-diuretic hormone causes your body to hang on to water rather than excreting it. So drinking the maximum 27 to 34 ounces of water could cause a net gain in water rather quickly, even if you're sweating. In this state, your kidney filtration rate can drop to as low as 100 milliliters hourly, or less than 3.5 ounces per hour. Under these extreme circumstances, drinking more than 3.5 ounces each hour could potentially cause problems. But depending on the amount you sweat and the exact level of the vasopressin hormone in your body, you may be able to drink more than this before feeling sick.
When you drink way more water than you need, electrolytes become imbalanced and cells swell up, a condition known as hyponatremia. You might become confused, dizzy and disoriented, if your brain cells become engorged with water. Fatigue, nausea, loss of appetite and restlessness can also occur. In severe cases, you might start hallucinating or having convulsions. If you experience any of these symptoms after guzzling water for extended periods of time, it’s possible that you drank way more than your body can handle. You need to get to the doctor right away. Although rare, hyponatremia can be fatal.