Water

You should be able to:

  1. Identify the chemical composition of water.

  2. Understand the functions of water within the body.

  3. Learn the recommendations for water and reasons why water intake may increase or decrease.

What is water?

Water is an inorganic molecule composed of covalently bonded hydrogen atoms and an oxygen atom. Due to the electronegativity of water, hydrogen-bonding polar molecules and charged molecules are readily dissolved in water.¹ Water composes 60% of human mass and is either intracellular or extracellular (within blood plasma or interstitial fluid).² Water is considered an essential nutrient for life. 

What are the functions of water?

Water is used as a medium for many processes within the body. Water acts as a solvent and can dissolve hydrophilic molecules (charged or polar covalent molecules).² Water serves as a medium for atoms to collide and bond and excretes waste products from the reactions. The body’s control of water is also profound. Water is tightly regulated by the kidneys with hormones such as aldosterone and antidiuretic hormone (ADH) to control water balance directly or indirectly.² Water helps maintain body temperature as it absorbs heat exceptionally well, and it is found within sweat when body temperature is elevated. Water also lubricates the joints and organs, allowing for smooth, sliding motions to occur. 

What is the recommended amount of water? 

The amount of water recommended can fluctuate due to environmental temperature, physical activity, age, and the presence of certain diseases. Water or fluid restrictions may be recommended if a person has fluid retention from certain diseases such as heart failure or kidney disease. An Adequate Intake (AI) is recommended for water. An AI establishes the recommended amount if an RDA cannot be determined. The following are Adequate Intake (AIs) recommended for total water (in both food, beverages, and drinking water) measured as liters/day³:



Other than drinking water, what other sources contain water?

Pure drinking water is the most hydrating method of obtaining water; however, other foods and beverages contain water as well. Non-starchy vegetables (such as tomatoes, lettuce, cucumbers, etc.) and fruits (watermelon, strawberries, peaches, oranges, etc.) contain a high percentage of water.² Foods such as popsicles, gelatin, ice cream, milkshakes, and soup are considered when counting water and fluid intake.² Drinks such as milk, juices, soda, and coffee also contain water but can be less hydrating compared to drinking water due to the presence of sugar, caffeine, and preservatives.

Source(s):

1. Jerry Tortora and Bryan Dickerson, Principles of Anatomy & Physiology, 16th ed. (New Jersey: John Wiley & Sons, 2021).

2. Denise M Medeiros and Robert E.C. Wildman, Advanced Human Nutrition, 4th ed. (Burlington, MA: Jones & Bartlett, 2019).

3. https://ods.od.nih.gov/HealthInformation/nutrientrecommendations.aspx#dri