We need water to survive. “Drink plenty of water” is a common health advice you have heard all your life. You have probably heard stories of people dying from lack of water. It is, therefore, hard to imagine that there is such a thing as water intoxication or water poisoning. Can you die from drinking too much water? Yes, you can but it is very rare. However, it is relatively common to see people admitted to the hospital after drinking too much water. In my 10 years of treating hospitalized patients, I have personally treated at least 10 patients with water intoxication symptoms. To understand how water intoxication happens and how much water is too much, you need to understand how your body regulates water.
Water intoxication: How your kidneys adapt to fluctuations in water intake
Your water intake fluctuates from day to day. You may drink a gallon of water a day when you are out on a hot sunny day. You many only drink a few cups of water on other days. Your body has a very sophisticated mechanism to adapt to varying amounts of daily water intake.
Your kidneys are the most important organs that maintain water balance. The amount of water in your blood (we will call the water component of the blood “blood water” in this article for convenience) determines its concentration of salt. The concentration of salt (more specifically Sodium; we will use the term salt and sodium interchangeably for this discussion) in blood water is extremely important for the normal functioning of your body organs.
Even a slight change (less than 2%) in blood water salt concentration can make you very sick. When the salt concentration in blood water goes down, water goes inside your organ cells and they swell up. The swelling of your brain can be dangerous and can cause many worrisome symptoms. Similarly, when the salt concentration in blood water goes up, it draws water out of your organ cells and they shrink. The rapid shrinking of your brain can be very dangerous.
After drinking too much water, that water gets absorbed into your blood. Without the rapid adjustment by your kidneys, that water would make your blood dilute. The average volume of blood water is about 3 liters (about 4/5 of a gallon). If you rapidly drink a gallon of water, that water gets absorbed into your blood. However, all that water does not stay in your blood vessels. Water and salt can freely go in and out of your blood vessels into a space called extracellular space. This is the space between your blood vessels and your organ cells. This space contains about 11 liters (2.9 gallons) of water. The concentration of salt in blood water and this extracellular water is same because both salt and water can flow freely between these spaces. However, your organ cells have a membrane that does not allow salt to go in or out freely. The movement of water between these two spaces is determined by the salt concentration of blood water (which is same as the salt concentration of extracellular space).
When you drink a gallon of water, that water goes into your blood and then to your extracellular space. Before you drank that gallon of water, the volume of blood water and extracellular water was 3.7 gallons (2.9 extracellular plus 4/5 blood water). After rapidly drinking that gallon of water, this volume would expand to 4.7 gallons (3.7 plus 1). Without intervention from your kidneys, this would cause a significant change in the concentration of salt in your blood water. To be precise, the concentration would change by 21%( 1 divided by 4.7). Such a large change in blood water salt concentration might kill you instantly from too much brain swelling secondary to water intoxication. Luckily, your kidneys will intervene and save your life.
Your kidneys have the ability to separate salt and water from your blood water. When the salt concentration of blood water goes up, kidneys take out the salt and make highly concentrated urine with the extra salt. When the salt concentration of blood water goes down, kidneys make very dilute urine with extra water. The ability of kidneys to make very dilute and very concentrated urine varies in different species of animals. The kidneys of animals that are adapted to desert can concentrate the urine many more times than we humans can.
There is a limit to how much and how fast your kidneys can make very dilute urine. If you are an average build young healthy person, your kidneys can filter about 90-120 milliliters (3 to 4 oz.) of blood water per minute. Most of this filtered water is reabsorbed and goes back into your blood. Within a certain limit, your kidneys can control the amount that gets reabsorbed. When more water is reabsorbed, your urine becomes concentrated. When less water is reabsorbed, your urine becomes dilute. In theory, normal human kidneys can dilute the salt content of the urine to about 1/6 the concentration of salt in blood water. At this dilution the maximum theoretical amount of urine you can produce in 24 hours is about 20 liters (about 5 and a quarter gallons). It appears that it would take your kidneys at least 4.6 (24 divided by 5,25) hours to get rid of that gallon of water. Assuming you have perfect kidneys, you can prevent water intoxication if you take your time and spend at least 4.6 hours to slowly finish that water.
So, can you drink a gallon of water a day? Yes you can, as long as you do not drink it fast enough. You can even get by drinking 5.25 gallons of water if you do it slowly and uniformly over a 24-hour period. However, this calculation assumes that you have a pair of perfectly working kidneys with good capability to produce maximally dilute urine. Your kidneys may not be fully capable of pushing its ability to the limits. In practice, I would recommend finishing a gallon of water over at least eight hours to avoid any chance of water intoxication. If you have known kidney problems, you may need to adjust even further.
What happens when you keep gulping water faster than that? You start to have water intoxication symptoms. The water goes down to your stomach and starts getting absorbed into your blood. Your blood starts to get a little dilute; your body gives a signal to your kidneys and they start working right away to produce maximum amount of dilute urine as fast as they can. As you keep drinking too much water, the kidneys can no longer excrete all the excess water. When you continue water intake at that rate, dilution of blood water begins. Your brain starts to swell up.
Symptoms of water intoxication:
Water intoxication symptoms start as soon as salt concentration of blood water drops down by about 3%. The first symptom is usually nausea. It may be your body’s way of telling you to stop drinking more. If you keep drinking past that, you will get other symptoms. You will feel weak and lethargic. Your may start to have headaches. As your blood water gets more dilute, your brain function gets compromised and you will become confused. Life threatening water intoxication symptoms appear when the salt concentration dips below 14-15% of normal. At that stage, even your heart and lungs stop working and you may die from water intoxication.
Water intoxication: What is the lethal dose of water?
The median lethal dose or LD50 of water has been calculated at 6 liters, which is about 1.6 gallons. The lethal dose calculation assumes that all of it is taken right away. LD50 is defined as the amount required to kill half of all test subjects. This dose calculation is not based on actual observation in humans and may not be very accurate.
As you can see, water intoxication and death from drinking too much water depends on the speed with which you drink it. You can drink the 1.6 gallons of water slowly over 24 hours without getting any water intoxication symptoms. However, if you drink it within an hour, you can die from water intoxication.
How do you treat water intoxication?
If you have concerns about someone having possible water intoxication symptoms, you need to get that person to the nearest ER right away. As I stated in the beginning of the article, I have treated a few of such patients. They need to be admitted to ICU for close monitoring. If the sodium concentration in the blood is only reduced by less than 3%, they can be just observed closely without access to any drinking water. We then check their sodium (salt) concentration every one or two hours to make sure they are trending in the right direction. We also check their urine sodium level to confirm the diagnosis. In patients with low blood salt from water intoxication, the urine salt level is always at the lowest possible level. If the urine salt concentration is high enough, we have look for diseases other than water intoxication that can cause low sodium.
If the sodium concentration were reduced more than 10%, the patient’s condition would be critical. We monitor those patients very closely and start treatment with IV infusion. We give salt solution that has a concentration of about 3.8 times the normal blood water salt concentration. When this highly concentrated salt mixes with the blood, blood salt levels start to rise up. We watch the patient very closely during this stage because correcting the salt level too fast can be dangerous. We do not want to shrink the swollen brain too fast. That can cause permanent damage to a part of the brain. We check the blood salt level every hour while closely monitoring the patient’s vital signs. We adjust the salt-water infusion rate to make sure we are slowly raising the salt level at an acceptable rate. Patients slowly improve with the treatment and become more awake and alert.
Water intoxication: Why would anyone drink too much water in the first place?
This is a good question. I sure hope you do not drink that much water after reading the dangers of water intoxication. However, it happens because some people do not know that even water can be dangerous. People think drinking water is good for health and push the limits. Sometimes people start drinking too much water because of some psychological problems. They may be anxious and depressed and somehow feel that drinking water would help them cleanse their problems. At other times, people may drink too much water when they are going through withdrawal from alcohol or drugs. They may be trying to detoxify themselves by flushing their bodies with water.
I hope you would share this article with your friends and family to raise awareness about potential dangers of water intoxication. Yes, water is good for you but too much of a good thing can sometimes be bad.