Adequate hydration is essential for overall health. Even minor fluid loss can negatively affect the body, particularly during intense physical activity, hot weather, or periods of heavy sweating.

Losing just 1–3% of body weight due to dehydration may impair mood, focus, and memory, and may increase the likelihood of headaches in some individuals.

Increasing water intake may help ease constipation, lower the risk of kidney stones, reduce some hangover symptoms, and support weight loss when consumed before meals.

Water makes up approximately 60% of the human body.

A commonly promoted guideline suggests drinking eight 8-ounce (237-mL) glasses of water daily, known as the “8×8 rule.”

While this recommendation lacks strong scientific evidence, staying well hydrated remains important for health.

Below are seven evidence-based benefits of drinking enough water.

1. Supports physical performance

Insufficient water intake can lead to reduced physical performance.

This becomes particularly important during intense exercise or exposure to high temperatures.

Losing as little as 2% of body water can impair performance. In athletes, sweat loss during training or competition may reach 6–10% of body weight.

Dehydration can interfere with temperature control, increase fatigue, reduce motivation, and make physical activity feel more demanding both mentally and physically.

Proper hydration helps prevent these effects and may reduce oxidative stress during high-intensity exercise. Since muscle tissue is made up of roughly 80% water, hydration plays a key role in performance.

Summary: Even small losses of body water can significantly impair physical performance.

2. Affects energy and brain function

Hydration status has a strong influence on brain performance.

Studies show that mild dehydration—defined as a 1–3% loss of body weight—can negatively affect mood, concentration, memory, and alertness.

In one study, young women who lost 1.4% of body fluid after exercise experienced worsened mood, reduced concentration, and more frequent headaches.

A similar study in young men found that a 1.6% fluid loss impaired working memory and increased feelings of anxiety and fatigue.

For someone weighing 150 pounds (68 kg), a 1–3% loss equals roughly 1.5–4.5 pounds (0.5–2 kg), which can easily occur during normal daily activities.

Multiple studies across different age groups show that even mild dehydration can impair cognitive performance and emotional well-being.

Summary: Mild dehydration can reduce energy levels, worsen mood, and impair mental performance.

3. May help reduce headaches

Dehydration is a known trigger for headaches and migraines in some people.

Headaches are among the most commonly reported symptoms of inadequate fluid intake.

Some research suggests that increasing water consumption may reduce headache severity and frequency in individuals who experience frequent headaches.

In a study of 102 men, those who increased daily water intake by 1.5 liters (50.7 ounces) reported improved migraine-related quality of life. Nearly half experienced headache improvement, compared with only 25% in the control group.

However, findings are mixed, and researchers note that more high-quality studies are needed.

Summary: Drinking more water may help relieve headaches, though further research is required.

4. May relieve constipation

Constipation is a common condition marked by infrequent bowel movements and difficulty passing stool.

Increasing fluid intake is often recommended as part of treatment, and research supports this approach.

Low water intake is associated with a higher risk of constipation in both younger and older adults.

Improved hydration can help soften stools and promote regular bowel movements.

Mineral water—particularly varieties high in magnesium and sodium—may be especially effective in improving stool frequency and consistency.

Summary: Adequate hydration may help prevent and relieve constipation, especially in people with low fluid intake.

5. May reduce kidney stone risk

Kidney stones are painful mineral deposits that form in the urinary system.

Some evidence suggests that higher water intake may lower the risk of kidney stone recurrence in people who have had stones before.

Drinking more water increases urine volume, diluting mineral concentrations and reducing the chance that crystals will form.

Water may also help prevent stones from forming initially, though more research is needed.

Summary: Increased water intake appears to reduce the risk of kidney stone formation.

6. Can help reduce hangover symptoms

Hangovers involve symptoms such as headache, fatigue, thirst, and dry mouth after alcohol consumption.

Alcohol acts as a diuretic, increasing fluid loss and contributing to dehydration.

While dehydration is not the main cause of hangovers, it contributes to many of their symptoms.

Drinking water between alcoholic drinks and having a large glass of water before bed may help reduce hangover severity.

Summary: Staying hydrated can help ease some common hangover symptoms.

7. May support weight loss

Drinking more water may help with weight management.

Water can increase feelings of fullness and slightly boost metabolic rate, leading to greater calorie expenditure.

In a study of 50 young women with overweight, drinking 500 mL (16.9 ounces) of water three times daily before meals for eight weeks resulted in significant reductions in body weight and body fat.

Timing matters as well. Drinking water about 30 minutes before meals appears most effective.

Another study found that individuals who drank water before meals lost 44% more weight over 12 weeks than those who did not.

Summary: Drinking water before meals may support weight loss by increasing satiety and boosting metabolism.

Bottom line

Even mild dehydration can have noticeable physical and mental effects.

Whether your daily target is 64 ounces (1.9 liters) or another amount, consistently drinking enough water is one of the simplest and most effective ways to support overall health. 💧