It may seem like a silly question, since water is probably one of the safest things you can drink, and drowning isn’t technically an overdose. It’s certainly not the sort of frippery that you’d expect to kick off Mind the Science Gap’s winter 2013 season (Welcome back!). After all, it’s water. Well, as any toxicologist worth his (or her!) salt will tell you, it’s the dose that makes the poison, and yes, you can overdose from drinking water. In fact, there’s a fair amount of medical literature out there on the subject because it’s not as uncommon as you might think.
The symptoms of water overdose – or, “water intoxication” as doctors and people with fancy coats call it – are similar to alcohol intoxication: headache, nausea, vomiting, confusion, drowsiness, and, in extreme cases, even death. Water overdose is most commonly associated with drug abuse and compulsive disorders, but it can occur whenever someone downs glass after glass of water in rapid succession. By drinking such large volumes of water so quickly, victims push their kidneys (which are nature’s pee-factories) into overdrive, causing them to pee excessively to get rid of it all the extra fluid. This wouldn’t be a problem, except that all that urine is carrying with it a bounty of salt that the body needs to function normally. As the balance of salt-to-water slips out of whack (the salt-to-water ratio in cells is called “osmolarity”), the drinker becomes intoxicated and experiences symptoms. Like alcohol intoxication, water intoxication is reversible, depending on the amount of liquid consumed, provided that the body is gradually given salt and has time to recover.
Water intoxication that results from drug abuse is typically caused by the abuse of either opiates or MDMA (also known as “ecstasy”). In the case of opiates, water overdose is caused the same manner I described earlier—opiates make users chronically thirsty, so they drink lots of water, leading to excessive peeing and so forth—but in the case of MDMA, it’s the result of excessive sweating. Since MDMA is often used as a party drug, abusers tend to take a lot of it and go out dancing for many, many hours, and because they know that they’re going to get dehydrated from dancing, they drink a lot of water. Since they’re losing tons of salt through their sweat and they’re not replenishing it because they’re only drinking water, the osmotic balances in their sweaty dancing bodies are ruined, and water intoxication ensues.
Okay, so it’s possible. Then how much is too much?
Well, it depends. The lethal dose of H2O varies from person to person and depends on a bunch of other factors: how much water you drank, how fast you drank it, what else you were consuming at the time (food, drugs, alcohol, deceptively-convincing pieces of plastic fruit), if you having any health conditions (illness, diabetes, pregnancy, ect.), or if it’s really hot out or if you’re at a high altitude, and oh man there are like a billion things.
This is all to say that, basically, drinking water is fine, and most people could stand to drink a little more water during the day – daytime fatigue is often dehydration in disguise – the key is to not drink a ton of it in one go. Just space that water out, you know? Your kidneys can safely pass a maximum 15 liters of water a day (about seven-and-a-half 2-liter bottles’ worth), but you shouldn’t drink that much anyway. The Mayo Clinic recommends the consumption of at least eight 8-ounce glasses of liquid per day, which should include some water, but can also include things like milk, or tea, or delicious, delicious grape juice.
Of course, if you’re sweating a lot, especially from work or exercise, you should probably drink more water than you normally would, and if you’re really going to town, also maybe a sports drink to replenish the sodium you lose from sweating.
In conclusion, yes, it’s possible to O.D. from drinking water. No, it’s not likely that you, personally, will do it. Yes, you and I should probably both consider drinking more water and less soda pop/coffee/hooch (well maybe the last one’s just me). And naturally, you should subscribe to the RSS feed and enjoy another glorious semester of MTSG! Down in front, now, no shoving! Plenty of science for everyone…
Radojevic, N., Bjelogrlic, B., Aleksic, V., Rancic, N., Samardzic, M., Petkovic, S., & Savic, S. (2012). Forensic aspects of water intoxication: Four case reports and review of relevant literature. Forensic science international.