In 2007 Jennifer Strange, age 28, took part in a on-air radio station water drinking contest. Over the course of three hours she consumed six liters of water (a bit over 1.5 gallons) and a few hours later died of water-intoxication. It is crazy that drinking water can be lethal, but as noted by Hans Rosling in has fantastic book Factfulness : “Actually, everything you need to survive is lethal in high dosage.”
How does drinking a lot of water kill someone? The medical term for water-intoxication is hyponatremia and it means that the concentration of sodium in your blood is abnormally low.
Usually, our kidneys control the balance of water and salts in the body, but when we drink too much water in a short period of time, the kidneys cannot filter out enough water from our bloodstream and the blood becomes overly diluted. The excess water moves to where there is a higher concentration of salts – in to cells – which expand like balloons to take on more water. This works okay in most parts of the body as there is room for cells to expand, but it does not work in the brain as there is nearly zero room for brain cells to expand and swell due to being packed inside our boney skulls along with cerebral fluid.
In our day-to-day lives hyponatremia is uncommon, but long bouts of exercise can cause both dehydration and hyponatremia. A 2005 study in the New England Journal of Medicine found that about 15% of marathon runners develop some degree of hyponatremia. As we exercise we sweat out salts in addition to water. If we take in only plain water while we are exercising, hyponatremia may result. As such, it is good practice to drink some sports drink (which contains electrolytes) during long exercise sessions.
Hyponatremia can also be caused by certain medications and some medical conditions. Symptoms of hyponatremia include confusion, headaches, nausea and bloating.
Both drinking not enough water and drinking too much are problematic. So, how much water should we drink a day? It varies person-to-person depending on factors such as what we eat, how much salt is in our diet, how active we are, how much we sweat. The idea that everyone should drink eight glasses of water a day is not supported by any scientific evidence. For some people it may not be enough while for others it might be way too much.
According to Scientific American, “as long as you are healthy and equipped with a thirst barometer unimpaired by old age or mind-altering drugs . . .drink to your thirst. It’s the best indicator.” Similarly, the Mayo Clinic advises: “Drinking water is vital for your health, so make sure you drink enough fluids. But don’t overdo it. Thirst and the color of your urine are usually the best indications of how much water you need. If you’re not thirsty and your urine is pale yellow, you are likely enough water.”
Finally, note that coffee, tea, other beverages and watery fruits and vegetables count toward fluid intake.
Here’s a daily water intake calculator from Cigna that can serve as a rough guide: Water Consumption Calculator