It's not uncommon for marathon runners to experience a condition called hyponatremia, or lack of salts in your blood. They run for miles and miles, losing sweat, and drink water to replace lost fluids but not the salts found in the sweat itself. That's when they start to experience symptoms, such as mental confusion and muscles not working properly. While you may think hydration is a good thing -- and it is -- marathon runners are the perfect example of how it is possible to drink too much water.
When you drink enough water to where the salts in your blood are severely diluted, you can experience a number of health concerns. The first symptoms may include headache, fatigue and feelings of nausea. As the levels of water in your body increase, you may vomit, urinate frequently and feel disoriented and confused -- a condition known as water intoxication. The changes in mental function are especially troublesome because extra water in your body can cause water to move into your cells, making them expand. While the cells in your tissues have room for expansion, the cells in your brain do not. Because your skull limits cell expansion, brain swelling can cause symptoms like seizures, respiratory arrest, coma and death.
Time Frame Considerations
One of the reasons why it is possible to drink too much water is because your kidneys can only filter so much fluid at a time. If your kidneys are healthy, you can filter about 800 to 1,000 mL or 0.21 to 0.26 gallons of water, meaning you can drink about this much every hour and have your kidneys function normally. The only exception is situations that are stressful to your body -- like marathon running -- when hormones in your kidneys signal the body to hold on to extra water. If you consistently drink more water than your kidneys can filter over a short time period, you are more likely to experience symptoms of water intoxication, even if you have not yet exceeded the daily maximum amount that causes water intoxication.
Putting It Together
When considering how much water healthy kidneys can filter in a day, you can filter about 15 L -- almost 60 glasses -- of water each day, according to Go Ask Alice!, a health resource from Columbia University. Staying under this level in your daily intake and using a hydration strategy that includes replacing electrolytes if you are an endurance athlete can ensure you do not experience adverse effects from drinking too much water.
Drinking too much water is not likely to occur if you follow a few rules of thumb concerning hydration, according to the Mayo Clinic. If you drink enough water to where you rarely feel thirsty and your urine is clear to yellow in color, you are likely drinking enough water and do not need to drink more. While the amount of water varies for every person, using these indicators as a rule of thumb can help you avoid excess water intake.