Does Drinking More Water Boost Your Energy?

Reaching for another coffee when you are tired is common, but would a glass of water help instead? Here is what studies say about hydration and energy, and a 7-day test to see what works for you.

In this article

1. Does drinking more water actually boost energy?
2. How does mild dehydration affect energy and mood?
3. How much water do you need each day?
4. Do coffee and tea count toward your fluid intake?
5. How can you tell if low fluid is behind your tiredness?
6. How can you test whether water changes your own energy?
7. Who should be careful about drinking more water?
8. Frequently asked questions
9. Final thoughts
10. Sources and further reading

Does drinking more water actually boost energy?

Drinking more water can improve how energetic you feel if you are mildly dehydrated, but there is little evidence it adds energy once you are well hydrated. Water does not supply calories, so it cannot fuel you directly. Its role in the hydration and energy link is about avoiding the dip that comes with fluid loss.

Most of the research here comes from short lab studies in healthy young adults. They ask what happens when people lose a small amount of fluid, not what happens when people who are already well hydrated drink more.

That distinction matters for everyday life. If you drink little during a busy day, a glass of water may help you feel more like yourself. If you already drink to thirst and eat regular meals, a fourth or fifth extra bottle is unlikely to make you feel noticeably livelier.

How does mild dehydration affect energy and mood?

Mild dehydration of around 1 to 2% of body mass has been linked, in controlled studies, to greater fatigue, lower vigor and a worse mood. Effects on thinking tests are smaller and less consistent. Most of these studies induced dehydration with exercise, sometimes with a diuretic, so they do not copy ordinary desk life exactly.

What did the study in young women find?

In a 2012 study in The Journal of Nutrition, Armstrong and colleagues tested 25 healthy young women (average age 23) across three controlled sessions. When the women reached at least 1% body mass loss (an average of 1.36%), they reported lower vigor, higher fatigue and more overall mood disturbance than when well hydrated.

They also reported that tasks felt harder, concentration was lower and headaches were more common. The authors noted that most aspects of cognitive performance were not affected. The sample was small and young, so the results may not apply to everyone.

What did the study in young men find?

A 2011 study in the British Journal of Nutrition by Ganio and colleagues followed 26 young men through similar trials. Mild dehydration increased fatigue and tension or anxiety. It also increased errors on a visual vigilance task (P = 0.048) and slowed response on a visual working memory task (P = 0.021).

What do reviews say about the bigger picture?

A 2012 review in the Journal of the American College of Nutrition by Adan reported that dehydration of about 2% can impair attention, psychomotor skills and immediate memory, while longer-term memory and executive function seem more preserved. The author also pointed to methodological inconsistencies that limit firm conclusions.

A 2022 systematic review of 24 trials with 493 athletes found clearer cognitive impairment at 3 to 5% body mass loss, usually with heat stress. Studies with smaller losses showed minimal changes, and the review described the evidence as inconsistent. In plain terms, the link between water and sharp thinking is real but modest and depends on how much fluid is lost.

How much water do you need each day?

The US adequate intake for total water is about 2.7 litres (91 ounces) a day for adult women and 3.7 litres (125 ounces) for men, counting all drinks and food. These figures come from a 2004 report by the Institute of Medicine, now part of the National Academies. They describe what adequately hydrated people typically consume, not a target for everyone.

Daily movement also shapes energy levels. is walking 10,000 steps a day really necessary? looks at how much activity the research supports.

The same report notes that roughly 80% of total water comes from drinks and about 20% from food. Very active people or those living in hot climates may need more.

Harvard Health makes a similar point from a different angle. It says most people need roughly four to six cups of plain water a day once other fluids and food are counted, and that there is no one-size-fits-all answer. The CDC likewise says needs vary by age, sex, pregnancy status, activity level and breastfeeding status.

Do coffee and tea count toward your fluid intake?

Yes, for most people moderate coffee and tea count toward daily fluid intake. Harvard Health states that all beverages contribute to hydration and that coffee and tea do not cause net dehydration. Water is still the simplest choice, since it adds no sugar or alcohol.

For the sleep side of the coffee question, see does caffeine really ruin your sleep?

A 2014 PLOS ONE crossover study by Killer, Blannin and Jeukendrup supports this. Fifty healthy men who usually drank three to six cups of coffee a day had four cups of coffee or water daily for three days. Blood and urine markers of hydration did not differ significantly between the two. The study included only men who were regular coffee drinkers, so it says less about people who rarely drink caffeine.

How can you tell if low fluid is behind your tiredness?

The NHS lists thirst, headache, light-headedness, dark yellow and strong-smelling urine, and peeing less often as common signs of dehydration. Tiredness can also be part of the picture. The NHS advises drinking enough during the day that your urine is a pale colour.

Tiredness has many causes besides fluids, including stress. how stress affects your heart rate covers one of the body's stress signals.

Harvard Health adds that older adults may not sense thirst as strongly as they once did, so they should not rely on thirst alone. Warning signs such as weakness, dizziness or confusion deserve medical attention rather than an extra glass at home.

What else commonly causes tiredness?

Low fluid is only one candidate. Short or broken sleep, skipped meals, long sitting, stress, low iron, thyroid problems, depression, infections and some medications can all make you feel flat. If tiredness lasts for weeks, is unusual for you, or comes with other symptoms, a clinician can look for causes that no amount of water will fix.

When is dehydration an urgent problem?

The NHS says to contact NHS 111 urgently for unusual tiredness with dizziness on standing or a big drop in urination, and to call 999 if dehydration brings confusion, difficulty breathing, cold skin or extreme drowsiness. Babies, children and older adults are at higher risk, so extra care is sensible for them.

How can you test whether water changes your own energy?

You can run a simple 7-day self-experiment: record your drinks, your urine colour and a daily energy score, then look for patterns. One week will not prove cause and effect, but it can show whether low-fluid days tend to be your low-energy days.

The last row of the table is deliberate. A good day and a bad day can both follow high water intake, which is why a log helps you avoid crediting water for something that sleep or food did.

Who should be careful about drinking more water?

People with kidney, liver, heart or thyroid conditions may need to limit fluids, and some medications affect fluid balance, so they should follow their clinician's advice. Harvard Health flags these groups and names NSAIDs, opioids and antidepressants among medicines that can affect fluid retention.

Pregnancy and breastfeeding change fluid needs, as the CDC notes. If you are pregnant, take regular medication or have a medical condition, ask your doctor or pharmacist how much fluid is right for you before changing your intake sharply.

Hot weather, fever, illness and hard exercise raise needs too. The CDC says the body requires more water in those situations. In those cases, sipping steadily and paying attention to symptoms is safer than forcing large amounts at once.

See a healthcare professional if you are constantly thirsty, pass very large amounts of urine, feel unusually exhausted for weeks, or have confusion, dizziness or fainting. These can have causes that go beyond drinking habits.

Frequently asked questions

Why am I still tired when I drink plenty of water?

Fluid is only one factor. Sleep, food, stress, activity, medications and health conditions all shape energy, and well-hydrated people can still feel flat. If your urine is pale and you drink to thirst, look at sleep and routine next. Persistent unexplained tiredness is worth raising with a doctor.

Does water help with the afternoon slump?

It might, if you have not drunk much since morning. Studies of mild dehydration link it to more fatigue and lower vigor, so a drink may help in that case. If you are already hydrated, the slump more likely reflects sleep, meal timing or body rhythms, and water alone probably will not fix it.

Does cold water or lemon water give more energy?

The sources reviewed for this article do not show that water temperature or lemon changes energy. The CDC suggests citrus wedges mainly as a way to make plain water taste better so you drink it more often. Choose whatever you will actually drink, ideally without added sugar.

Should I drink water first thing in the morning?

You can, and many people find it a handy habit, but the research reviewed here does not single out morning water as special. Total fluid across the day matters more. If your first urine of the day is dark and you feel thirsty, a glass is reasonable.

Does food count toward my daily water?

Yes. The Institute of Medicine report found that roughly 20% of total water intake comes from food, with the rest from drinks and plain water. The CDC also notes that water-rich foods such as fruits and vegetables contribute, which is one reason eight glasses is not a universal target.

Can a smartwatch or band tell me if I am dehydrated?

Not directly. Wearables estimate things like heart rate and activity, not how much fluid you have lost, and they should not replace thirst, urine colour or medical advice. Used with your own written drink log, they can help you spot personal patterns over time.

Final thoughts

Here is the short recap.

• Mild dehydration is linked with more fatigue and a worse mood in controlled studies, so water helps mostly when you are short on fluid.
• There is little evidence that drinking extra water beyond your needs adds energy.
• Coffee and tea count toward your fluid intake, and needs vary with activity, heat and health.

Your turn: Have you noticed a difference in your energy when you drink more water? Tell us in the comments.

Sources and further reading

1. Armstrong LE, Ganio MS, Casa DJ, et al. Mild dehydration affects mood in healthy young women. The Journal of Nutrition, 2012.
2. Ganio MS, Armstrong LE, Casa DJ, et al. Mild dehydration impairs cognitive performance and mood of men. British Journal of Nutrition, 2011.
3. Adan A. Cognitive performance and dehydration. Journal of the American College of Nutrition, 2012.
4. Systematic review. Effects of hypohydration and fluid balance in athletes' cognitive performance: a systematic review. PubMed Central, 2022.
5. Killer SC, Blannin AK, Jeukendrup AE. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLOS ONE, 2014.
6. Institute of Medicine (National Academies). Report sets dietary intake levels for water, salt and potassium to maintain health and reduce chronic disease risk. National Academies, 2004.
7. Harvard Health Publishing. How much water should you drink? Harvard Health.
8. NHS. Dehydration. NHS website.
9. Centers for Disease Control and Prevention. Water benefits, tips, and intake. CDC.