We Asked a Doctor If Drinking More Water Can Actually Boost Your Energy

Many people reach for coffee or an energy drink when they feel sluggish, but plain water is often overlooked. Even mild dehydration can affect how you feel physically and mentally, sometimes before thirst kicks in.

To better understand whether plain water can actually increase energy—or simply help you feel better—we spoke with Joseph Mercola, DO, a board-certified family physician and author of “Your Guide to Cellular Health”.

*This interview has been edited and condensed for length and clarity.

Q: Can drinking plain water actually give you more energy?

Mercola: Yes, it can. When you’re even slightly dehydrated, your body’s ability to produce energy drops. Research shows that fluid loss as low as 1% to 2% of your body weight slows down blood flow and reduces oxygen delivery to your brain and muscles. That means less energy, both physically and mentally.

Dehydration also interferes with how your brain uses dopamine and serotonin—the chemical messengers that help regulate mood, focus, and motivation. So you may feel sluggish or irritable before you even realize you’re thirsty.

Drinking water helps restore blood volume, supports neurotransmitter function, and improves oxygen delivery. The result is a real, measurable boost in energy levels, not just a placebo effect.

Can Drinking Water Help You Feel Better Overall?

Absolutely. Water doesn’t just affect energy; it impacts everything from stress levels to emotional balance.

When you’re dehydrated, your body releases vasopressin, a hormone that signals the kidneys to conserve water. But vasopressin also helps trigger cortisol, your main stress hormone. That means dehydration can raise your stress response, even if you’re not consciously anxious.

Drinking water helps lower these stress signals and supports a calmer, more stable mood. In fact, research shows that people who drink less than 1.5 liters of water a day have significantly higher cortisol spikes during stressful events compared to those who stay well-hydrated.

It also improves brain function by restoring blood flow and neurotransmitter balance. That can reduce headaches, clear mental fog, and even ease symptoms like irritability and confusion.

Even if your energy doesn’t noticeably improve right away, your nervous system becomes less reactive, and that can make a big difference in how you feel overall.

Why Does Dehydration Affect Energy So Much?

Energy production depends on efficient circulation, oxygen delivery, and cellular function—and dehydration disrupts all three.

When fluid levels drop, blood volume decreases, which slows circulation and limits how much oxygen and glucose reach the brain and muscles. This can lead to physical fatigue, slower reaction time, and mental fog, even before you feel noticeably thirsty.

Dehydration also affects the nervous system and brain signaling. With less fluid available, nerve communication becomes less efficient, and the brain has to work harder to carry out routine tasks.

On a cellular level, water is required for metabolic reactions that produce energy. When cells don’t have enough usable water, those processes become less efficient, making everyday activities feel more draining.

The takeaway: Even mild dehydration can shift the body into a lower-energy state, which is why drinking water can sometimes restore clarity and stamina rather than simply quenching thirst.