Understanding Hydration

H. Ali, PhD
H. Ali, PhD
November 21, 2023
min read
Technically reviewed by: 
Diagnox Staff
Understanding Hydration

What is Hydration?

Hydration refers to the state of maintaining adequate fluid levels in the body. It represents a balance between water, electrolytes, nutrients, and other compounds essential for various bodily functions. Both insufficient fluid replacement (hypohydration) and excessive fluid intake (hyperhydration) can significantly impact your health and well-being.

How to Measure Hydration?

The body's hydration level can be assessed through various methods, including plasma osmolality and urine specific gravity (USG). USG can be measured using a refractometer or a dipstick reagent test. Dipstick tests are a quick, practical, and non-invasive way to determine USG. They are particularly useful for monitoring hydration status in various settings, including home, sports, and exercise contexts.

When immersed in a urine sample, the dipstick's reagent pad reacts and changes color, reflecting the urine's specific gravity. This change indicates the body's hydration status, categorizing it as over-hydrated, optimally hydrated, minimally dehydrated, significantly dehydrated, or severely dehydrated. It is the same kind of test professionals frequently use in their practice.

Testing hydration levels can involve simple methods like observing the color of urine, monitoring the frequency of urination, and being aware of thirst cues. Hydration test strips from Diagnox offer a more precise method using urine specific gravity measurements.

What do the USG results mean?

Typically, a urine specific gravity (USG) within the range of 1.002 to 1.030 is considered clinically normal. It's not uncommon for results to fall slightly outside this range. The higher the USG value, the more concentrated the urine is. For reference, the specific gravity of plain water is 1.000.

Urine specific gravity (USG) is a measure of the concentration of electrolytes and other substances in your urine, relative to the amount of water. USG also indicates how effectively our kidneys concentrate urine and maintain optimal nutrient, electrolyte, and fluid balance.

From a clinical perspective, this wide 'normal' range for USG may not align with the optimum range for a healthy individual, especially athletes or people who regularly engage in physical activity or exercise. Given the rapid loss of water and electrolytes during physical exertion, even slight variations in USG can quickly lead to abnormal levels. This can significantly impact physical performance and may increase the risk of injury.

What are Different Levels of Hydration?

Different levels of hydration can be inferred depending on your USG reading::

1. Overhydration

  • USG: Less than 1.005
  • Very low values suggest overhydration, characterized by an excess of water relative to solutes. This can dilute essential electrolytes and increase the risk of hyponatremia, where blood sodium levels are abnormally low.
  • In diabetes insipidus, kidneys lose the ability to concentrate urine, leading to low USG. People consuming diuretic medications or substances like coffee and alcohol may also have low USG.

2. Optimal Hydration (Euhydration):

  • USG: 1.005 - 1.010
  • Euhydration refers to the state of optimal total body water content, regulated by the brain, where the kidneys efficiently dilute urine to eliminate waste products while minimizing excessive water loss
  • Urine within this range is typically light in color, resembling pale straw or light yellow. This is commonly used as a visual indicator of good hydration.

3. Boderline/Mild Dehydration:

  • USG: 1.011 - 1.020
  • Values in this range indicate minimal dehydration. This may be a sign that the body is beginning to conserve water, likely due to insufficient intake or increased fluid loss, such as through sweating.
  • Urine becomes more concentrated and may appear yellow. Early signs of dehydration, like dry mouth or thirst, may occur, and it is advisable to increase fluid intake accordingly.

4. Significant Dehydration:

  • USG: 1.021 - 1.030
  • Indicates a significant deficit in fluid levels (3% to 5% dehydration), often due to intense exercise, illness, or reduced fluid intake. This could be accompanied by physical signs such as decreased skin turgor, lethargy, and reduced urine output.
  • The urine may appear amber in color. Active rehydration strategies are usually necessary.

5. Severe Dehydration:

  • U-SG: Greater than 1.030
  • Signifies severe dehydration, where the kidneys concentrate urine to the maximum extent possible to preserve the body's remaining fluid. The urine may be a shade of brown or dark orange.
  • Severe dehydration is a medical emergency as it can result in hypovolemia, electrolyte imbalances, and kidney damage if not promptly treated. Immediate medical attention and intervention with oral or intravenous fluids are critical to restore hydration balance.

Recommended Hydration Level for Athletes

For athletes, pregame hydration status is crucial for optimizing performance. Studies indicate that about 50% of individual and team-sport athletes are dehydrated at the start of competition [1]. Even a 1% to 2% dehydration of body weight can start to impact performance. Dehydration exceeding 3% of body weight significantly disturbs physiological functions and increases the risk of exertional heat illnesses, such as heat cramps, heat exhaustion, or heat stroke [2].

It's recommended that physically active individuals maintain euhydration, which is within +1% to -1% of body weight. This corresponds to a urine specific gravity (USG) of 1.005 to 1.010. Given the substantial sweat loss that can occur in competitive sports within a short period, maintaining euhydration with minimal variation is essential. This status allows the body to efficiently regulate temperature and maintain cardiovascular function during intense physical activity.

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Why Measuring Hydration is Important?

Testing hydration levels is crucial for several reasons, particularly in ensuring overall health, optimizing physical performance, and preventing dehydration-related health issues. The importance of measuring and maintaining optimum hydration includes:

  • Supports Cellular Function: Every cell in the body needs water to function correctly. Water is vital for cellular homeostasis and biochemical reactions. Both poor hydration and over-hydration can adversely impact cellular functions, organ health, and the entire body.
  • Enhances Physical Performance: For athletes and those engaged in physical activities, optimal hydration is crucial for peak performance. Both dehydration and overhydration can compromise athletic performance during exercise and competitive sports. Dehydration can reduce strength, focus, and increase the risk of injury, as well as escalate cardiovascular stress during intense exercise. Conversely, over-hydration due to excessive intake of fluids can increase the risk of bloating, gastrointestinal discomfort, and body mass gain – all undesirable traits during sports or any physical activity.
  • Promotes Mental Clarity and Cognitive Function: Hydration status significantly impacts cognitive function, concentration, and mood. Even mild dehydration can affect cognitive abilities, impair attention, judgment, and memory. Scientific evidence suggests that both under and over-hydration can dull the ability to perceive and interpret sensory information.
  • Assists in Metabolism, Weight Management, and Digestive Health: Adequate hydration is vital for digestion, promoting satiety, nutrient absorption, supporting gut health, and preventing digestive issues like constipation, gastritis, ulcers, and acid reflux.
  • Supports Kidney Function: Proper hydration is crucial for kidney/renal health for the effective removal of waste, toxins, and excess substances from the body. Staying well-hydrated helps in maintaining a healthy glomerular filtration rate (GFR), a measure of how well the kidneys are filtering blood. Dehydration can reduce GFR, indicating impaired kidney function. Chronic dehydration can lead to higher concentrations of calcium and other minerals in the urine, which can precipitate and form kidney stones. Optimal hydration helps prevent kidney stones by increasing urine flow and diluting substances in the urine. Adequate fluid intake also helps prevent UTIs by flushing bacteria from the urinary tract.
  • Helps Toxin Elimination: Optimal hydration supports the body's natural detoxification systems, including the kidneys, liver, digestive system, lymphatic system, and skin. It aids in eliminating toxins and waste products through urine, feces, and sweat and is essential for overall health and efficient bodily functions.
  • Ensures Nutrient Transport: Blood, composed of approximately 90% water, plays a vital role in transporting oxygen and various nutrients (such as glucose and amino acids) to cells and in removing waste products like carbon dioxide. Adequate hydration maintains proper blood volume for efficient circulation, ensuring effective nutrient transportation and absorption, and supporting the health of vital organs and tissues.
  • Provides Thermoregulation: Optimal hydration is essential for effective thermoregulation. It enables adequate sweat production, maintains blood volume for heat dissipation, prevents heat stress conditions, supports cardiovascular function, and contributes to overall body temperature stabilization. This is particularly important in hot environments and during physical activities that increase body heat [3].
  • Prevents Overhydration. Overhydration or hyponatremia can be just as dangerous as dehydration. Excessive water intake can put you at risk of water intoxication or hyponatremia, where sodium levels diminish, causing swelling in organs and tissues.

Who should test hydration levels?

Testing hydration levels for wellness monitoring is beneficial for various groups of people, each with specific needs or circumstances that make monitoring their hydration status particularly important:

  • Athletes and physically active individuals.
  • People with certain health conditions, such as UTIs, diabetes, heart, and kidney diseases.
  • Older adults.
  • People working in hot climates.
  • Individuals trying to manage weight.
  • Patients in clinical settings, especially those with fluid restrictions or receiving diuretic therapy.
  • Pregnant and breastfeeding women.
  • People with a history of hyponatremia.
  • Individuals engaged in high-altitude activities.

In general, while everyone should be mindful of their hydration, these specific groups may need to pay extra attention due to their increased risk of either dehydration or overhydration.

How Often Should I Measure My Hydration Levels?

Body hydration levels are dynamic, meaning they fluctuate throughout the day. For instance, first-morning urine is generally more concentrated, typically resulting in a higher USG value. Factors like fluid intake, diet, climate, hormonal (circadian) rhythms, and activity levels significantly influence your body's hydration status.

A spot urine test provides a snapshot of your hydration status at a specific moment. For a comprehensive hydration profile, it's advisable to monitor USG multiple times throughout the day. Relying on a single data point for a conclusive assessment can be misleading.

For clinical evaluation using USG measurements, it is recommended to check urine specific gravity on a 24-hour urine sample for a more accurate and comprehensive analysis.


All physiological systems in the human body are influenced by our hydration level. Optimal hydration is essential for maintaining body temperature, lubricating joints, and enabling the transportation of nutrients and oxygen to cells. It supports metabolic functions, aids in digestion, and facilitates the removal of waste and toxins. Moreover, staying well-hydrated is critical for cognitive functions, affecting mood, concentration, and memory; it is also fundamental for muscular endurance and overall physical performance. Scientific studies show that dehydration can impair aerobic capacity, muscle endurance, and mental performance. It also elevates the likelihood of suffering from heat exhaustion and heat stroke. Chronically atypical USG is linked to several serious medical conditions, including diabetes insipidus, hypertension, and renal stenosis, among others.

  1. McDermott BP, et al., “National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active,” J Athl Train. 2017;52(9):877-895.
  2. James LJ, et al., “Does Hypohydration Really Impair Endurance Performance? Methodological Considerations for Interpreting Hydration Research,” Sports Med. 2019;49(Suppl 2):103-114.
  3. Montazer S, et al., “Assessment of Construction Workers' Hydration Status Using Urine Specific Gravity,” Int J Occup Med Environ Health. 2013;26(5):762-9.

About the Author
H. Ali, PhD

Hussnain Ali received his Ph.D. degree in EE in 2015 from the University of Texas at Dallas, USA. He is the co-founder and the Chief Executive Officer (CEO) at Diagnox Health, Plano, TX 75024, USA, and a visiting research scientist at the University of Texas at Dallas. His academic and industry experience spans over 15 years in organizations like the Center for Advanced Research in Engineering, The University of Texas at Dallas, and Harman/Samsung. He has served as a co-PI on an RO1 grant from the National Institutes of Health (NIH). His research interests include biomedical devices, auditory rehabilitation, and cochlear implants. He has authored and co-authored over 70 international publications and has been awarded multiple US patents. His latest work at Diagnox encompasses the development of innovative healthcare and wellness products/solutions that provide convenient and affordable at-home screening/diagnosis. He aims to bridge conventional clinical diagnostic products with Artificial Intelligence (AI) and contemporary data-centric technologies to modernize the healthcare and wellness industry.

About the Reviewer
This blog was
Technically reviewed by: 
Diagnox Staff

Diagnox Staff consists of a multidisciplinary team of scientists, content writers, and healthcare professionals with an expertise to create and review high-quality, informative, accurate, and easy-to-understand content for both professionals and everyday readers. Our staff follows strict guidelines to ensure the credibility and authenticity of the information, reviewing them independently and verifying them by various scientific and technical sources to ensure accuracy. Our review team believes in delivering knowledge free from bias to improve public health and well-being.

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