Overhydration: What Happens If You Drink Too Much Water?

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Your body needs the right amount of fluids to function but drinking too much of it can lead to overhydration. Drinking fluids to excess can cause serious harm to your health, especially if minerals in your body called electrolytes drop too low too fast.

Let’s dig deeper into what causes overhydration, symptoms to look out for, who’s at risk for the condition and how to treat it.

What Is Overhydration?

Overhydration happens when you drink very large volumes of fluids such as water and your body holds onto more than your kidneys can excrete in your urine. This causes fluids to build up in your bloodstream and body tissues.

Knowing how to calculate how much water to drink daily can help keep you from overhydrating. But even if you go over your usual daily fluid needs, chances are you won’t develop overhydration symptoms. 

The body tightly regulates fluid balance in many ways. This means overhydration happens for many reasons. That said, overhydration can lead to a fluid imbalance in your body and dilute vital substances in your blood such as electrolytes.

Are There Different Types of Overhydration?

In order to fix overhydration, you need to know the process that can cause it. Broadly speaking, the 2 different types involve drinking more fluids than your kidneys can get rid of and retaining too much fluids in your blood.

For instance, certain people may be more prone to drinking excess amounts of fluids. These include:

  • Endurance athletes and people engaged in intense and prolonged physical activity who drink large volumes of fluids without replacing key electrolytes such as sodium (salt)
  • People with primary polydipsia, especially those with the type seen in people with a psychiatric illness called psychogenic polydipsia
  • Those with heat illness or dehydration

Or, people may retain too much water due to health issues such as:

  • Diabetes
  • Heart failure
  • Kidney disease
  • Liver disease
  • Medication side effects
  • Premature infants with immature kidneys
  • Syndrome of inappropriate antidiuretic hormone (SIADH)

What Causes Overhydration?

Drinking large amounts of fluids isn’t the sole cause of overhydration. The kidneys play a vital role in fluid balance in the body. It’s no surprise then that kidney disease is more common in those who overhydrate. 

But it isn’t easy to overhydrate, especially if you don’t have any health issues that impact your heart, kidneys, liver or pituitary glands. For instance, your average young adult with no kidney- or heart-health issues would need to drink more than 6 gallons of fluids daily to overhydrate.

Primary Polydipsia

Primary polydipsia can lead to drinking too much water. People with various psychiatric illness are prone to the psychogenic type of this condition.

These include people with:

This can cause you to urinate way more often. In turn, this can lead to a condition caused by low levels of sodium in your blood called hyponatremia.

The other type is called dipsogenic polydipsia — also called compulsory water drinking. This happens most often in people who consciously drink large amounts of water to support a healthy lifestyle. It’s also seen in some people with damage to a part of the brain called the hypothalamus.

Polydipsia and overhydration can lead to an extreme form of hyponatremia called water intoxication — also known as water poisoning or toxicity. These can lead to dire symptoms that affect your body and brain.

Syndrome of Inappropriate Antidiuretic Hormone

Hydration status is also linked to the pituitary gland. This gland sits at the base of your brain and is attached to your hypothalamus.

The pituitary gland secretes a hormone called antidiuretic hormone, which causes you to retain fluids. This less common cause of overhydration is known as SIADH.

Various medicines, surgeries, hormone issues, genes and some cancers such as a type of lung cancer called small cell lung cancer can cause SIADH. So can some types of illness and disease such as HIV, pneumonia and stroke.

Who’s at Higher Risk for Overhydration?

People whose kidneys don’t excrete urine normally are at higher risk of overhydration. Also at risk for overhydration are people who take certain medicines that could cause polydipsia or SIADH. These include medicines for depression.

What Are the Symptoms of Overhydration?

The symptoms of overhydration are caused by low sodium levels in your bloodstream. The body aims to keep your sodium levels within a normal range, that is between 135 and 145 milliequivalents per liter. 

This is because our brain cells are very sensitive to changes in sodium levels. If it drops too low, brain cells called neurons begin to swell. 

Mild to moderate overhydration that occurs slowly tends to cause milder symptoms. These include feeling tired and having a hard time staying focused.

Vomiting and balance problems can develop when overhydration happens quickly. As your condition gets worse, you may:

  • Feel more confused
  • Have seizures
  • Lapse into a coma

And if you overhydrate but the fluid levels in your blood stay normal, the excess fluids often move into your cells. This can cause tissue swelling called edema. When your blood volume gets too high, fluids can build up in your lungs and lower legs.

What Are the Complications of Overhydration

The most severe complication of overhydration is cerebral edema or brain swelling. Excess fluids cause your neurons to swell. This raises the pressure in the part of your skull that covers your brain called the cranium.

This is referred to as increased intracranial pressure (ICP). It can cause symptoms such as:

In some cases, ICP can lead to coma and even death. 

How to Diagnose Overhydration

Your doctor will talk with you about your medical history, current medications and symptoms. Next, they’ll examine you for signs of edema and weight gain. 

They’ll also discuss how much fluids you’ve been having each day. And, they’ll likely run urine and blood tests to check your electrolyte levels, especially the level of sodium in your blood.

How to Fix Overhydration

Treatment for overhydration depends on its cause, as well as which symptoms you have and how severe they are. These treatments may include:

  • Restricting daily fluids to less than a quart until your sodium levels and symptoms improve over the course of a few days
  • Replacing sodium if you have severe hyponatremia
  • Stopping medicines causing your symptoms
  • Treating the underlying condition that caused you to overhydrate

You may also need to limit how much salt you have for a few days if you’re retaining fluids because of heart, kidney or liver issues. This is because salt causes your body to retain more fluids.

It’s best to treat overhydration in these ways under the watchful care and guidance of your doctor. They will monitor you to be sure you stay safe and that treatments are working. If you have severe hyponatremia or water toxicity, you’ll likely be admitted to the hospital to be cared for and closely monitored by your health care team. 

How to Prevent Overhydration

If you’re generally healthy, you can figure out your daily fluid needs using this water calculator. Keep in mind that your usual fluid needs may change based on your:

  • Activity level and duration
  • Age
  • Weather conditions

Your health status also plays a role. If you have any health issues that affect your heart, kidneys or liver, your doctor can clarify how much fluids and sodium you need daily to stay healthy and prevent overhydration.