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Regardless of how much water is lost through sweating, urination and/or respiration, there is an upper limit of water a person can drink per hour. This limit is determined by the capacity of the kidneys to filter the water. Drinking above that in a short period of time may result in death.
Real life examples of water intoxication
In 2007, a woman died in a water drinking competition called “Hold Your Wee for a Wii“, where contestants had to drink a 250ml bottle of water every 15 minutes without urinating. The quantity of water was then increased to half liter bottles.
In total, she is believed to have drunk 7.5 liters within a short period of time. She died later that day from water intoxication.
There have been other reported cases of water intoxication in the past few decades, whether by endurance athletes or by club-goers taking drugs while dancing and getting overly thirsty due to excessive sweating. (1)
One study involving blood samples of 488 Boston Marathon runners has shown that 13% experienced hyponatremia and 0.6% a severe hyponatremia at the finish line. (1)
Symptoms of drinking too much water
The normal concentration of sodium in the blood is between 135 and 145 millimoles per liter.
Hyponatremia (water intoxication) is a condition where the level of sodium (and other electrolytes) in the blood gets diluted with too much water.
Some common symptoms of water intoxication are headache, nausea, vomiting, muscle spasms, frequent urination, hallucinations, fatigue, mental disorientation and seizures.
These symptoms can be detectable when the sodium concentration in the blood reaches 120 millimoles per liter, but are usually associated with 110 millimoles per liter. (2)
Severe water intoxication can be deadly and can occur when the concentration of sodium falls below 105 millimoles per liter.
Why you can “drown” from drinking too much water?
The kidneys filter the blood and decide how much water and solutes, including sodium, stay in the body and how much are excreted through urine.
It has the capacity to filter between 800 to 1000 ml of water per hour.
Drinking more than that cause an excess of water inside the body, due to the kidneys inability to filter this excess.
The result is hyponatremia (low sodium concentration in the blood) which can cause swelling of the brain and lead to death. (2)
The additional water travels to places where the concentration of sodium and other solutes is greater.
This process is called osmosis – solutes attract water.
With an excessive amount of water in the blood, the highest concentration of those solutes is in the cells rather than in the blood.
Therefore, the excess water moves from the blood to the cells, causing the cells to swell.
Neurons (also known as brain cells) unlike other cells, that are flexible enough to withstand an extra influx of water, cannot expand.
They are tightly packed within the bony skull with no possibility of expansion.
Through a rapid influx of water, the brain starts to swell, causing seizures, coma, acute delirium, respiratory arrest, hernia in the brain stem and death. (2)
How do you know how much you sweat?
For the athletes who lose excessive amount of water through sweating, balancing water intake is especially important.
To avoid water toxicity, it is a good idea to know how much they sweat during exercise to better control their water intake.
There are many tools on the web to calculate the sweat rate. I included in the references section an example of such a calculator. (3)