• The human body comprises around 60% water.
  • It’s commonly recommended that you drink eight 8-ounce (237-mL) glasses of water per day (the 8×8 rule).
  • Although there’s little science behind this specific rule, staying hydrated is important.
  • Here are 7 evidence-based health benefits of drinking plenty of water.

1. Helps maximize physical performance

  • If you don’t stay hydrated, your physical performance can suffer.
  • This is particularly important during intense exercise or high heat.
  • Dehydration can have a noticeable effect if you lose as little as 2% of your body’s water content. However, it isn’t uncommon for athletes to lose as much as 6–10% of their water weight via sweat.
  • This can lead to altered body temperature control, reduced motivation, and increased fatigue. It can also make exercise feel much more difficult, both physically and mentally.
  • Optimal hydration has been shown to prevent this from happening, and it may even reduce the oxidative stress that occurs during high-intensity exercise. This isn’t surprising when you consider that muscle is about 80% water.
  • If you exercise intensely and tend to sweat, staying hydrated can help you perform at your absolute best.

2. Significantly affects energy levels and brain function

  • Your brain is strongly influenced by your hydration status.
  • Studies show that even mild dehydration, such as the loss of 1–3% of body weight, can impair many aspects of brain function.
  • In a study in young women, researchers found that fluid loss of 1.4% after exercise impaired both mood and concentration. It also increased the frequency of headaches.
  • Many members of this same research team conducted a similar study in young men. They found that fluid loss of 1.6% was detrimental to working memory and increased feelings of anxiety and fatigue.
  • A fluid loss of 1–3% equals about 1.5–4.5 pounds (0.5–2 kg) of body weight loss for a person weighing 150 pounds (68 kg). This can easily occur through normal daily activities, let alone during exercise or high heat.
  • Many other studies, with subjects ranging from children to older adults, have shown that mild dehydration can impair mood, memory, and brain performance.

3. May help prevent and treat headaches

  • Dehydration can trigger headaches and migraines in some individuals.
  • Research has shown that a headache is one of the most common symptoms of dehydration. For example, a study in 393 people found that 40% of the participants experienced a headache as a result of dehydration.
  • What’s more, some studies have shown that drinking water can help relieve headaches in those who experience frequent headaches.
  • A study in 102 men found that drinking an additional 50.7 ounces (1.5 liters) of water per day resulted in significant improvements on the Migraine-Specific Quality of Life Scale, a scoring system for migraine symptoms.
  • Plus, 47% of the men who drank more water reported headache improvement, while only 25% of the men in the control group reported this effect.
  • However, not all studies agree, and researchers have concluded that because of the lack of high-quality studies, more research is needed to confirm how increasing hydration may help improve headache symptoms and decrease headache frequency.

4. May help relieve constipation

  • Constipation is a common problem that’s characterized by infrequent bowel movements and difficulty passing stool.
  • Increasing fluid intake is often recommended as a part of the treatment protocol, and there’s some evidence to back this up.
  • Low water consumption appears to be a risk factor for constipation in both younger and older individuals.
  • Increasing hydration may help decrease constipation.
  • Mineral water may be a particularly beneficial beverage for those with constipation.
  • Studies have shown that mineral water that’s rich in magnesium and sodium improves bowel movement frequency and consistency in people with constipation.

5. May help treat kidney stones

  • Urinary stones are painful clumps of mineral crystal that form in the urinary system.
  • The most common form is kidney stones, which form in the kidneys.
  • There’s limited evidence that water intake can help prevent recurrence in people who have previously gotten kidney stones.
  • Higher fluid intake increases the volume of urine passing through the kidneys. This dilutes the concentration of minerals, so they’re less likely to crystallize and form clumps.
  • Water may also help prevent the initial formation of stones, but studies are required to confirm this.

6. Helps prevent hangovers

  • A hangover refers to the unpleasant symptoms experienced after drinking alcohol.
  • Alcohol is a diuretic, so it makes you lose more water than you take in. This can lead to dehydration.
  • Although dehydration isn’t the main cause of hangovers, it can cause symptoms like thirst, fatigue, headache, and dry mouth.
  • Good ways to reduce hangovers are to drink a glass of water between drinks and have at least one big glass of water before going to bed.

7. Can aid weight loss

  • Drinking plenty of water can help you lose weight.
  • This is because water can increase satiety and boost your metabolic rate.
  • Some evidence suggests that increasing water intake can promote weight loss by slightly increasing your metabolism, which can increase the number of calories you burn on a daily basis.
  • A 2013 study in 50 young women with overweight demonstrated that drinking an additional 16.9 ounces (500 mL) of water 3 times per day before meals for 8 weeks led to significant reductions in body weight and body fat compared with their pre-study measurements.
  • The timing is important too. Drinking water half an hour before meals are the most effective. It can make you feel more full so that you eat fewer calories.
  • In one study, dieters who drank 16.9 ounces (0.5 liters) of water before meals lost 44% more weight over a period of 12 weeks than dieters who didn’t drink water before meals.