Everyone has experienced it: you go hours without drinking water and begin to feel odd. Your throat may become parched and irritated; perhaps your muscles feel tense. Yet internally, even greater changes occur: cells begin to contract as water departs from them, and the kidneys start preserving water, causing urine to darken.

The solution is simple: drink more water. Still, many neglect this fundamental aspect of self-care; 24% of older adults in the U.S. experience some level of dehydration, according to a recent . “Water is involved in every bodily process, so overlooking it means missing major chances to enhance health,” explains Jodi Stookey, a nutrition epidemiologist at the San Francisco Department of Public Health who researches hydration. While guidelines differ—the popular eight glasses daily rule —Stookey advises roughly one liter per day for most adults.

Below are five unusual indicators that you should increase your water intake.

Moodiness and brain fog

The brain is among the first organs impacted by insufficient water intake. Even slight dehydration—defined as losing as little as in water—can , working memory, and reaction speed. Individuals remain capable of performing tasks, yet they often become more moody, short-tempered, and anxious—especially women, notes Stookey. Research suggests people may when inadequately hydrated. “The brain is extremely responsive to fluid levels, and decreased plasma volume can modify cerebral blood flow and neurotransmitter function,” states Lawrence Judge, assistant dean at Florida Gulf Coast University’s Marieb College of Health & Human Services.

Headaches and dizziness

Insufficient hydration causes headaches. This occurs because decreased fluid consumption can —especially brain regions that control pain—while disrupting electrolyte balance. Both factors can lead to head discomfort and dizziness, according to Judge.

Digestive slowdown and constipation

Water is crucial for propelling material through your digestive tract. When consumption is insufficient, the colon extracts more water from waste, resulting in harder, less frequent bowel movements. Prolonged inadequate hydration is a to constipation, Judge notes. A 2024 also revealed that proper water consumption is vital for preserving bacterial and immune balance in the gut, maintaining strong protection against .

Elevated heart rate and less endurance

When hydration declines, blood volume diminishes, compelling the heart to pump harder to sustain cardiac output. This can elevate resting heart rate, intensify weakness and tiredness, and diminish stamina—even during routine tasks, not just workouts. Simply walking your dog might cause a racing heart and lightheadedness if you’re dehydrated, and your workout could feel doubly difficult. “Greater dehydration impairs muscle function,” says Stookey. “You fatigue more quickly during physical activity.”

Skin changes that mimic aging

While increasing water intake won’t eliminate wrinkles, dehydration can cause skin to look lackluster, lose elasticity, and develop fine lines more easily. Indeed, pinching skin and observing how quickly it returns to form—assessing its elasticity—is one method medical professionals can . Proper hydration preserves skin elasticity and bolsters barrier function, influencing overall appearance.

Increased risk of getting sick

Fluid deficiency impairs the body’s capacity to combat pathogens and sustain immune cell performance. Chronic underhydration is linked to .

A 2023 examined three decades of data from nearly 12,000 adults and discovered a link between blood sodium levels—which rise when fluid consumption drops—and chronic disease. The research revealed that adults with or exhibit markers of accelerated biological aging compared to those with mid-range levels. This underscores the significance of long-term hydration—indicating that proper fluid balance plays a unique role in maintaining health and longevity.