Cedars-Sinai Blog

Superhydration: How Much Water Is Too Much?

Male soccer player drinking water after nighttime game with friends

With the sports and fitness crowd, it's a familiar mantra: hydrate, hydrate, hydrate.

In the proper amounts, water protects us from brain fog, mood changes, constipation and other ills that can arise from even slight amounts of dehydration. It helps regulate our body temperature, lubricates our joints, and removes waste through sweat, urine, and bowel movements.   

Since we get so many benefits from this calorie-free beverage, you might think that if drinking water is good for you, drinking more might be better.

"Is water good for you? Absolutely. Does drinking more than you need to replace water weight losses improve your workout? Almost certainly not," says Dr. Joshua Scott, a primary care sports medicine specialist with the Cedars-Sinai Kerlan-Jobe Institute.

"In fact, there's a significant amount of danger in doing that," he cautions.

This is because superhydrating—drinking large amounts of water over a long period of time—can put you at risk for hyponatremia, a condition caused by abnormally low levels of sodium in the bloodstream.

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Joshua C. Scott, MD

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Joshua C. Scott, MD

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"If I work out for an hour on a stationary bike and then get on the scale and see I'm down 5 pounds, I haven't lost 5 pounds of fat. I've lost 5 pounds of water weight."

The dangers of drinking too much water

Symptoms of hyponatremia include nausea and fatigue and can progress quickly to confusion, seizure and, in rare cases, death.

Dr. Scott uses the example of improperly trained marathon runners who down water at every aid station along the course and take a long time to cross the finish line. Over that extended time, they lose salt through sweat and, by ingesting so much water, they dilute what sodium is left in their bodies.

"If you exercise or do a sports activity for more than an hour, you need to replace not just water, but also sodium. This might mean having a sports drink or even a salty snack," Dr. Scott says.

Other electrolytes—essential minerals such as potassium and calcium—can be supplied through your daily diet, advises Dr. Scott.

Healthy hydration

The amount of water you need depends on many factors. These include your chosen activity, the intensity level and duration of your workout, your health status, and environmental conditions such as heat and humidity in the area you are working out in.

Since everyone sweats in different amounts and loses different rates of salt in their perspiration, it can be difficult to take a one-size-fits-all approach to hydration, Dr. Scott warns.

However, there are some basic guidelines for hydrating before, during, and after your workout or sport activity:

1. Start out fully hydrated: This means drinking about 24 ounces of water two to three hours prior to your workout or sport activity.

2. Weigh yourself: Before starting your exercise, take a moment to weigh yourself and record that measurement. You'll use this information to determine how much water you need post-exercise.

3. Think 12:30: During exercise, drink about 6 ounces of fluid every 15 minutes, or 12 ounces every 30 minutes.

"It's important that your hydrating drink has both carbohydrates and some electrolytes—specifically sodium," Dr. Scott says.

"A drink containing 6%-8% carbohydrates with at least 110 mg of sodium per every 8 ounces is good. It gives you that bit of energy you need and replaces water and sodium losses."

4. Weigh your water loss: When you've finished your activity, weigh yourself again. The difference between your pre- and post-exercise weight lets you know how much water you've lost.

"If I work out for an hour on a stationary bike and then get on the scale and see I'm down 5 pounds, I haven't lost 5 pounds of fat. I've lost 5 pounds of water weight. For someone who weighs 100 pounds, that indicates 5% dehydration," Dr. Scott says.

5. Rehydrate: Rehydrate your body by drinking about 16-24 ounces of fluid for every pound of water weight lost.

Hydration for those with certain health conditions

People with health conditions such as congestive heart failure or kidney disease are at risk of overhydration because their bodies may not clear fluid as quickly as someone without these conditions.

If you have an underlying health concern, it's best to consult with your doctor about your individual needs prior to participating in any activity, Dr. Scott says.

Dehydration and performance

Many of the benefits people equate with hydration are related to preventing dehydration. Even mild levels of dehydration (1%-2%) can cause premature fatigue and mood disturbances and impair physical motor skills.

At 2%-4% dehydration, your agility and sport-specific skills, such as shooting basketballs, will be impaired, says Dr. Scott.

Why hydration is important

By hydrating appropriately for your activity level and health, you'll avoid dehydration while reaping the many benefits of exercise.

"Our job at Cedars-Sinai Kerlan-Jobe Institute involves taking care of elite athletes who exercise at a much higher level than maybe the rest of us do, but the recommendations are still the same," Dr. Scott says.

"Start your workout fully hydrated, prevent dehydration by drinking fluids throughout your exercise, and then replace water losses afterward before starting a new day or a new workout."