How Much Water Should You Drink for the Biggest Benefits

by | Fitness, Nutrition

We’ve analyzed the available research and summarized the most important takeaways. What we found is that most online recommendations are far from accurate.

Optimal water intake is determined by a few criteria. Each one is discussed separately. You'll learn how to make the best choices based on your unique needs and lifestyle.

But first, let’s talk about the risks of under and over-consumption.

What Does It Mean to Be Dehydrated?

Dehydration levels of 7-10% are considered life-threatening [1]. However, measuring your exact state of hydration is surprisingly difficult. But you don’t need lab equipment to know your water intake is too low.

If you’re feeling thirsty you’re already dehydrated. Changes in urine production is another great sign. Dark color, strong smell, and decreased production mean you’re not drinking enough liquids. Those are all early signs you’ll feel around 0.5% dehydration.

Higher levels of water loss may include symptoms like:

  • dry mouth
  • headache
  • dizziness and lethargy
  • lack of sweating
  • weakness in muscles
  • shriveled and dry skin
  • fever and delirium

Note that even 1-2% dehydration will require drastic changes compared to your usual state. Rapid water loss can happen because of:

  • profound sweating
  • diarrhea
  • vomiting
  • certain medical conditions (e.g. diabetes)

Under normal conditions, you’ll rarely reach any dangerous levels of dehydration.

How Bad Is Prolonged Dehydration for the Brain?

Your brain is affected by water intake. However, it makes a notable difference just how hydrated you are.

Mild dehydration can affect your mood [2]. But your capacity to handle daily tasks won’t take a huge hit. You may not even notice any difference.

The more you limit your intake the higher the chances of diminished cognition and focus [3]. Children and the elderly may be affected to a greater extent. Probably because they are less adapted to manage their water balance.

Unless we’re talking about severe dehydration brain performance is only mildly affected. A poor night of sleep will have a bigger impact. It’s even more likely to happen. Most people find it harder to get 8 hrs of quality sleep than to remember to drink when thirsty.

Does Water Intake Affect Energy Levels & Physical Performance?

Many professional athletes undergo rapid dehydration to make weight before a weigh-in. This is probably the best example of how water intake affects  physical performance.

The period between the weigh-in and the event is not enough to restore normal water balance Yet, the benefit of making weight while operating in a sub-optimal hydration level is apparently worth it [4].

Note that different types of training are affected to a different degree. Let’s examine the two main types:

Strength Training

Contrary to popular belief, lifting weights is barely affected by your water intake. Dehydration levels of 3-5% rarely result in any notable changes in force production [5] [6] [7] [8]. Note that a typical session will rarely lead to more than 2-3% water loss.

Current research suggests that short strength training sessions are not affected by water intake. However, longer and more demanding sessions may take a hit if you’re not well hydrated [9].

This is probably because longer sessions deplete more of your water reserves. Body temperature and sweating increase, hence total water loss increases as well.

Unless your sessions are super long and you forgot your water bottle, dehydration is not a huge problem. If free access to water is allowed trainees naturally maintain their water balance.

Endurance Training

Sports like marathon running result in greater levels of dehydration compared to strength sports. This is why hydration is very important when it comes to endurance sports.

However, mild dehydration doesn’t result in performance decrease [10]. Endurance training suffers only when water intake is severely limited or prohibited. If people are allowed to determine their own intake they tend to drink just enough to stay competitive [11].

Interestingly enough, if you rely on body signals to regulate water intake you’ll be mildly dehydrated. But those signals are accurate enough as to not let dehydration reach levels that impact performance.

Unless you’re actively restricting water consumption training won’t suffer. The key here is that you have easy access to water during a session. Unlike strength training, it’s much harder to push through a workout if you drink no water.

How Much Water Is Too Much?

Drinking excessive amounts of water can cause hyponatremia. That's a condition characterized by low sodium concentration in the blood (135 mmol/L or less).

Increased liquid consumption leads to high water turnover rate. This results in sodium and other essential electrolytes (e.g. magnesium, potassium, and calcium) to be flushed out with urine.

What Are the Dangers of Overhydration?

Overhydration is very common among athletes [12]. It’s rarely justified and often does more harm than good. In fact, extreme cases of hyponatremia can cause death [13].

As we already showed, mild dehydration doesn’t impact performance in any notable way. However, “common knowledge” dictates we’re not drinking enough water. This is why some people may go to extremes to deal with their (unjustified) fear of dehydration.

Overhydration can disrupt the normal electrolyte balance. Depending on which electrolytes are affected you can observe some of the following symptoms:

  • irregular heartbeat
  • changes in blood pressure
  • nervous system disorders
  • weakness, lethargy, and fatigue
  • twitching, convulsions and muscle spasms
  • complete loss of appetite
  • bone disorders
  • moodiness and irritability
  • stomach pain and vomiting
  • confusion
  • seizures

Do Other Liquids Count Towards Your Daily Intake?

Yes. But that’s an incomplete answer. Depending on your diet composition more than half of your water intake can be coming from food.

Viscous and even solid foods sometimes contain huge amounts of liquids. For example, a cucumber is 90% water. Fruits and veggies are generally high in H20. Meat also contains some, but most of it evaporates when cooking.

Anything from soda, coffee, tea to salad, apples, and cooked rice counts towards your water intake.

How Do I Calculate My Water Intake?

You can find plenty of research and articles promoting one idea or another. But let’s think logically. How do you know which source to trust?

Water is vital for survival. Even more so than food. If we weren’t capable of solving the problem of water intake we would have been long extinct.

Yes, some adaptions serve is no good anymore (e.g. high sugar cravings vs sugar abundance in today’s world). But our needs and water availability didn’t change much

The body is exceptionally good at maintaining its water balance [14]. You really have to go out of your way to upset that equilibrium. This often means forcing yourself to drink when you clearly don’t feel like it. Or consciously deprive yourself despite feeling thirsty.

Liquid intake shouldn’t be rocket science. Listen to your body and go by feel. If you’re getting too dehydrated you’ll know. If you had too much, you’ll also know.

What Other Factors Determine My Daily Needs

Water requirements will vary depending on current needs and lifestyle. Here a few factors that can influence your intake:

  • bodyweight and size: smaller individuals have lower water requirements. They’re also less prone to overheating so they sweat less often.
  • food and diet: if you consume foods with high water content your liquid intake may go down
  • temperature: when you’re hot your water requirements may go up due to increased sweating. Body temperature can rise because of environmental factors or exercise.

You don’t need to consciously adjust your liquid intake to account for lifestyle changes.  The body is well adapted to detect changes in water turnover. Just listen to the signals it's giving you.

A Couple of Exceptions

Aging may result in a decreased responsiveness to thirst [15]. Slightly increasing your water intake is a good idea past a certain age.

Note that different people will be affected to a different degree. You can observe changes in urine to determine if drinking to thirst is still an accurate way to maintain water balance.

Exercising when the temperature is very low can also affect thirst responsiveness [16]. However, the effect is acute. Thirst signaling will go back to normal once the temperature rises to comfortable levels.

Does Drinking a Lot of Water Help You Lose More Fat?

Unfortunately, water has no weight loss properties, nor it speeds up your metabolism. There are few ways you can change your metabolism and it’s not as easy as drinking an extra gallon a day.

But staying well-hydrated can help curb hunger. One of the signals that triggers hunger reduction is stomach expansion. Your body responds to the volume of food consumed to determine when you had enough.

Food consistency does matter as well. But if you’re stuffed, your cravings will likely go down regardless of what you ate. In fact, even filling yourself with water will have a similar effect. As long as the stomach expands you’ll experience hunger reduction [17].

Diet adherence is the most important aspect of any weight loss program So drinking a few extra glasses of water can sometimes be justified. Just be sure to not overdo it.

Going to the toilet every 20 mins is not exactly great (see the sections above). Use water intake strategically before meals. This will limit the risk of overeating. When hunger is in check, don’t force yourself to drink more than needed.

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[1] Muscle contraction velocity, strength and power output changes following different degrees of hypohydration in competitive olympic combat sports

[2] Mild dehydration affects mood in healthy young women

[3] Effects of Dehydration on Brain Functioning: A Life-Span Perspective

[4] Muscle contraction velocity, strength and power output changes following different degrees of hypohydration in competitive Olympic combat sports

[5] Hypohydration effects on skeletal muscle performance and metabolism: a 31P-MRS study

[6] Impact of dehydration on a full body resistance exercise protocol

[7] Effect of hydration state on strength, power, and resistance exercise performance

[8] Hydration and muscular performance: does fluid balance affect strength, power and high-intensity endurance?

[9] The effects of fluid loss on physical performance: A critical review

[10] Comparison of Two Fluid Replacement Protocols During a 20-km Trail Running Race in the Heat

[11] Self-selecting fluid intake while maintaining high carbohydrate availability does not impair half-marathon performance

[12] Fluid and electrolyte balance during two different preseason training sessions in elite rugby union players

[13] Are we being drowned by overhydration advice on the Internet?

[14] Body fluid changes, thirst and drinking in man during free access to water

[15] Mechanism of attenuated thirst in aging: role of central volume receptors

[16] Thirst sensations and AVP responses at rest and during exercise-cold exposure

[17] Intragastric balloon-induced satiety is not mediated by modification in fasting or postprandial plasma ghrelin levels in morbid obesity.

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