Sleep is one of the most talked-about aspects of health, yet millions of people still wake up feeling unrefreshed. According to the Centers for Disease Control and Prevention, about one in three adults in the United States does not get enough sleep each night (1). 

Stress, technology use, and late-night habits are often blamed, but another factor receives far less attention: hydration. The amount of water you drink during the day may quietly influence both how long you sleep and how restorative that sleep feels.

What Does the Research Say About Water and Sleep?

A recent study titled Effects of Fluid Intake on Sleep Duration and Quality Among Healthy Adults examined whether hydration status influences sleep (2). Researchers recruited 15 healthy adults between 18 and 40 years of age. Participants completed two separate four-day monitoring periods. During the first period, their hydration levels were tracked under normal drinking habits. During the second period, participants intentionally reduced fluid intake to induce mild dehydration.

To capture precise sleep data, participants wore Oura Ring® devices, which recorded:

  • Total sleep time
  • Sleep efficiency
  • Time spent in the different sleep stages, including rapid eye movement (REM)

Hydration status was measured using 24-hour urine samples and urine specific gravity testing, allowing researchers to compare sleep outcomes under hydrated and dehydrated conditions.

Among participants who became successfully dehydrated, several patterns emerged:

  • Higher fluid intake was associated with longer total sleep time
  • Greater water consumption correlated with better sleep efficiency
  • The strongest effect was observed in REM sleep duration, with a correlation coefficient of 0.8, indicating a strong relationship.

The study concluded that mild dehydration alone did not significantly affect sleep in healthy young adults. However, overall fluid intake showed positive associations with REM sleep, sleep duration, and sleep efficiency. 

Some of these associations weakened after strict statistical adjustment, but the findings still suggest may play a meaningful role in sleep quality. Since REM sleep is necessary for learning, memory, and emotional regulation, adequate hydration may be an important yet often underappreciated factor in supporting restorative sleep.

Why Is REM Sleep So Important for Mental and Physical Health?

REM sleep is a highly active brain state. During this stage, cerebral blood flow and metabolic activity in many brain regions approach waking levels (3). REM sleep is also the stage most associated with vivid dreaming and plays a key role in cognitive and emotional processing.

What REM sleep helps with

  • Memory integration. Communication between the hippocampus and neocortex during sleep supports the stabilization and integration of new memories. REM contributes alongside non-REM sleep, depending on the type of memory involved (4).
  • Emotion recalibration. REM sleep is linked to overnight reductions in amygdala reactivity to prior emotional experiences, supporting next-day emotional steadiness (5).
  • Brain waste clearance (sleep-wide, mainly NREM). Metabolite clearance, including β-amyloid, is enhanced during sleep, most prominently during slow-wave/NREM/. This benefit is best attributed to healthy sleep architecture overall, rather than REM sleep alone (6).
  • Creativity and problem-solving. Experimental research suggests REM sleep (vs quiet rest or NREM) can enhance the formation of distant associations and creative problem-solving skills (7). 

How much REM do we typically get

Adults usually spend 25% of total sleep time in REM sleep,  about 90–110 minutes per night, with REM periods getting longer in the second half of the night (8).

What Happens to Sleep When You’re Dehydrated?

Dehydration affects several body systems that help regulate sleep. Even mild dehydration can raise heart rate, disrupt temperature control, and cause uncomfortable dryness in the mouth or throat. These changes make it harder to get truly restorative sleep.

Some common dehydration-related sleep disturbances include:

  • Dry mouth or throat, which may cause discomfort and increase awakenings (9).
  • Muscle cramps, especially if electrolyte loss is involved, can potentially cause sleep interruptions (10) (though this is more likely when dehydration is moderate or in physically active people).
  • When someone becomes severely dehydrated, their body loses too much fluid, including fluid from the bloodstream (11).
  • Lighter sleep or early morning awakenings (12)

How Much Water Do You Really Need Each Day?

How Much Water Do You Really Need Each Day?

Hydration needs depend on sex, weight, climate, and activity level. The National Academies of Sciences, Engineering, and Medicine recommends (13):

  • Men: 3.7 liters (125 ounces) of fluids daily
  • Women: 2.7 liters (91 ounces) of fluids daily

About 20% of daily fluid intake typically comes from the foods we eat, including:

  • Fruits such aswatermelon, oranges, and grapes
  • Vegetables like cucumber, lettuce, and celery)
  • Soups and yogurt

Other important considerations:

  • Athletes or people in hot climates need more fluids. Losing just 2% of body weight in sweat can impair cognition and sleep quality (14).
  • Timing matters: drinking large amounts close to bedtime often causes nocturia (night-time urination), which interrupts sleep (15).
  • Practical hydration check: Pale yellow urine usually signals adequate hydration, while darker urine suggests the body needs more fluid (16).

Consistent hydration throughout the day, rather than at night, gives the body what it needs to sustain restorative sleep.

What Foods and Drinks Can Help You Stay Hydrated?

Choosing water-rich foods and the right beverages can help with mood, energy, and sleep. Here are foods and drinks with good evidence for boosting hydration:

Water-rich foods (17):

  • Cucumber
  • Watermelon 
  • Strawberries
  • Leafy greens (lettuce, spinach, etc.)
  • Soups or broth-based meals

Hydrating beverages (12):

  • Plain water remains the go-to for hydration.
  • Herbal teas (caffeine-free) like chamomile and peppermint contribute fluids without caffeine’s stimulant or diuretic effects.
  • Coconut water can be useful after exercise or heavy sweating due to its potassium and electrolyte content
  • Milk may promote longer-lasting hydration than water alone in some studies because of its protein, fat, and electrolyte content

Drinks/ingredients to moderate (18, 19:

  • Alcohol: Increases urine output, disrupts sleep architecture, and worsens hydration
  • Sugary sodas and energy drinks: High sugar and caffeine can impair hydration and interfere with sleep quality.

What Other Lifestyle Factors Interact With Hydration and Sleep?

Hydration does not act in isolation. Diet, activity level, environment, stress, and health conditions all influence how fluids affect sleep.

Dietary patterns. High-sodium diets can increase thirst and nocturia. Reducing sodium intake has been associated with fewer nighttime bathroom trips. Diets rich in fruits, vegetables, and whole foods provide both water and electrolytes such as potassium and magnesium (20).

Physical activity. Sweating increases fluid needs. High-intensity exercise close to bedtime can hinder sleep onset, especially if rehydration is inadequate. 

Environment. Heat and low humidity increase water loss. Indoor heating and air conditioning dry out the air, which can increase airways dryness (21). 

Medical conditions. Fluid needs depend on health status. People with advanced chronic kidney disease (CKD) often need to monitor and limit their fluid intake. Those with diabetes typically benefit from personalized medical guidance around hydration. In obstructive sleep apnea, relieving airway or mouth dryness improves comfort and makes treatment easier to tolerate. While proper hydration won’t reduce apnea severity itself, it does help with sleep quality (22, 23). Consulting with a clinician ensures the hydration plan fits individual health needs.

Why Choose The Insomnia and Sleep Institute of Arizona for Sleep Health?

The Insomnia and Sleep Institute of Arizona knows sleep isn’t simple. Yes, stress and daily habits affect how you rest, but our evaluations look deeper at things like hydration levels, sleep apnea, or whether your internal clock is off.

Our board-certified sleep physicians bring both expertise and genuine care to every appointment. We use detailed testing polysomnography and home-based studies to figure out what’s actually going on with your sleep. From there, your treatment plan is built on solid medical evidence: cognitive behavioral therapy for insomnia, fine-tuning your CPAP, or exploring options like the Inspire implant.

What sets us apart:

  • Experienced doctors: Board-certified professionals oversee every step of care.
  • Accurate testing: Reliable tools help identify the true causes of poor sleep.
  • Practical solutions: Plans address health factors such as hydration, nutrition, and stress.
  • Accessible services: With offices in Scottsdale, Gilbert, and Phoenix, we provide care across Arizona through in-person visits and telemedicine.

The Insomnia and Sleep Institute of Arizona is a trusted resource for patients struggling with fatigue, disrupted sleep, or persistent concerns. With medical expertise, proven therapies, and genuine care, we help patients restore healthy, lasting sleep.  Contact us today. 

References

  1. CDC. (2016). CDC Newsroom. CDC. https://archive.cdc.gov/www_cdc_gov/media/releases/2016/p0215-enough-sleep.html
  2. Fein, T., Garay, J., & Voss, M. (2025). Effects of Fluid Intake on Sleep Duration and Quality Among Healthy Adults. Nature and Science of Sleep, Volume 17, 791–800. https://doi.org/10.2147/nss.s511807
  3. Rushd F.M. Al-Shama, Uleman, J. F., Pereira, M., Claassen, J. A. H. R., & Dresler, M. (2024). Cerebral blood flow in sleep: A systematic review and meta-analysis. Sleep Medicine Reviews, 77, 101977–101977. https://doi.org/10.1016/j.smrv.2024.101977
  4. Cox, R., Rüber, T., Staresina, B. P., & Fell, J. (2020). Phase-based coordination of hippocampal and neocortical oscillations during human sleep. Communications Biology, 3(1). https://doi.org/10.1038/s42003-020-0913-5
  5. Els van der Helm, Yao, J., Dutt, S., Rao, V., Jared M. Saletin, & Walker, M. (2011). REM Sleep Depotentiates Amygdala Activity to Previous Emotional Experiences. Current Biology, 21(23), 2029–2032. https://doi.org/10.1016/j.cub.2011.10.052
  6. Xie, L., Kang, H., Xu, Q., Chen, M. J., Liao, Y., Meenakshisundaram Thiyagarajan, O’Donnell, J., Christensen, D. J., Nicholson, C., Iliff, J. J., Takano, T., Deane, R., & Maiken Nedergaard. (2013). Sleep Drives Metabolite Clearance from the Adult Brain. Science, 342(6156), 373–377. https://doi.org/10.1126/science.1241224
  7. Cai, D. J., Mednick, S. A., Harrison, E. M., Kanady, J. C., & Mednick, S. C. (2009). REM, not incubation, improves creativity by priming associative networks. Proceedings of the National Academy of Sciences, 106(25), 10130–10134. https://doi.org/10.1073/pnas.0900271106
  8. Patel, A. K., Reddy, V., Shumway, K. R., & Araujo, J. F. (2024, January 26). Physiology, Sleep Stages. Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK526132/
  9. Shishira Sreenivas. (2017, June 28). Waking Up With Dry Mouth: What to Know. WebMD. https://www.webmd.com/oral-health/sleep-apnea-dry-mouth-causes
  10. Bordoni, B., Goldin, J., & Kavin Sugumar. (2025, September 14). Muscle Cramps. Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK499895/
  11. Taylor, K., & Tripathi, A. K. (2025, March 5). Adult Dehydration. Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK555956/
  12. Asher Y Rosinger, Anne-Marie Chang, Orfeu M Buxton, Junjuan Li, Shouling Wu, Xiang Gao, Short sleep duration is associated with inadequate hydration: cross-cultural evidence from US and Chinese adults, Sleep, Volume 42, Issue 2, February 2019, zsy210, https://doi.org/10.1093/sleep/zsy210
  13. Read. (2026). The National Academies Press. https://doi.org/10.17226//11537
  14. Riebl, S. K., & Davy, B. M. (2013). The Hydration Equation. ACSM’S Health & Fitness Journal, 17(6), 21–28. https://doi.org/10.1249/fit.0b013e3182a9570f
  15. Leslie, S. W., Sajjad, H., & Singh, S. (2024, February 17). Nocturia. Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK518987/
  16. Urine colour chart. (2026). Nsw.gov.au. https://www.health.nsw.gov.au/environment/beattheheat/Pages/urine-colour-chart.aspx
  17. Godman, H. (2024, July). Using food to stay hydrated – Harvard Health. Harvard Health. https://www.health.harvard.edu/staying-healthy/using-food-to-stay-hydrated
  18. McCullar, K. S., Barker, D. H., McGeary, J. E., Saletin, J. M., Gredvig-Ardito, C., Swift, R. M., & Carskadon, M. A. (2024). Altered sleep architecture following consecutive nights of presleep alcohol. SLEEP, 47(4). https://doi.org/10.1093/sleep/zsae003
  19. Archive: Study Links Shorter Sleep and Sugar-Sweetened Drink Consumption. (2016, November 9). Archive: Study Links Shorter Sleep and Sugar-Sweetened Drink Consumption | UC San Francisco. https://www.ucsf.edu/news/2016/11/404796/study-links-shorter-sleep-and-sugar-sweetened-drink-consumption
  20. Johnson, T. M. (2020). The chicken‐or‐egg dilemma with nocturia: Which matters most, the water or the salt? Journal of Clinical Hypertension, 22(4), 639–641. https://doi.org/10.1111/jch.13828
  21. Katarzyna Byber, Radtke, T., Norbäck, D., Hitzke, C., Imo, D., Matthias Schwenkglenks, Puhan, M. A., Dressel, H., & Mutsch, M. (2021). Humidification of indoor air for preventing or reducing dryness symptoms or upper respiratory infections in educational settings and at the workplace. Cochrane Database of Systematic Reviews, 2021(12), CD012219–CD012219. https://doi.org/10.1002/14651858.cd012219.pub2
  22. Kennedy, B., Lasserson, T. J., Wozniak, D. R., & Smith, I. (2019). Pressure modification or humidification for improving usage of continuous positive airway pressure machines in adults with obstructive sleep apnoea. Cochrane Database of Systematic Reviews. https://doi.org/10.1002/14651858.cd003531.pub4
  23. Georg Nilius, Domanski, U., Schroeder, M., Woehrle, H., Graml, A., & Franke, K.-J. (2018). Mask humidity during CPAP: influence of ambient temperature, heated humidification and heated tubing. Nature and Science of Sleep, Volume 10, 135–142. https://doi.org/10.2147/nss.s158856

 

Disclaimer: The information provided in this blog post is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always consult with a licensed healthcare provider for recommendations specific to your individual health needs.