What Happens When You Drink Too Much Water?

As John Mayer might say, your body is a water-land.  According to the US Geological Survey, water makes up about 73 percent of human brains and hearts, 83 percent of human lungs, 79 percent of muscles and kidneys, and up to 60 percent of the human body overall. So much of you is made of water that just drinking the stuff should probably count as liquid cannibalism. You are what you eat? More like you drink what you are.

And drink you must. Water is essential to cell-building, temperature regulation, respiration, digestion, and other vital bodily processes. It even provides a protective buffer for your brain. But how much H2O must you drink? And what happens if you drink too much?

To answer those questions, it's important to establish what "too much" means in this context. Per ThoughtCo, healthy adults can expel about 15 liters (approximately 4 gallons) of water in a day, which is about five times as much water as an average man needs to drink (3 liters) and almost seven times as much as what the average woman needs (2.2 liters). However, the danger of overhydrating doesn't come from how much water you drink in a day, but rather how fast you drink.

If you drink loads of water in a short period of time, it can result in an electrolyte imbalance that causes your body to mimic the symptoms of alcohol intoxication. That's right — you'll get drunk on water. At first blush that sounds like an economic replacement to beer pong, but ThoughtCo explains that "water intoxication produces the same effects as would result from drowning in fresh water." Your body's "cells could swell to the point of bursting." 

Tissue swelling could exert so much force on your brain that you might become comatose or even die. This isn't just theoretical. CBS reported that in 2014, a pair of high school football players died of overhydration. One of them consumed 2 gallons of water and an additional 2 gallons of Gatorade after a single practice. 

The issue of overhydration is further complicated by the role of exercise, which, according to Scientific American, can drastically limit your kidneys' ability to excrete excess water because of the body's stress response to physical exertion. So while the average healthy kidney might expel 800 to 1,000 milliliters of water an hour, that capacity might drop all the way down to 100 milliliters while you're running a marathon. Even if you seem to be sweating buckets, it's possible to dangerously overhydrate. 

Overall, the best way to know when you've had enough water is to listen to your body. If you're not thirsty, you don't need to guzzle the wet stuff.