Water is necessary to sustain life and maintain health. Chemically, water has the formula of H2O, and is known as hydrogen oxide. Water comprises most of the human body, although the proportion of water varies by age, body fat, body mass, and gender (Marieb & Hoehn, 2013). Infants have 73% or more water (Marieb & Hoehn, 2013). Healthy male adults have 60% of their body mass as water, and healthy female adults have 50% water (Marieb & Hoehn, 2013). Water content declines with age to about 45% in older adults (Marieb & Hoehn, 2013). It comprises 90% of most cells in the body, except in adipose cells, which are up to 20% water (Marieb & Hoehn, 2013; Pizzorno & Murray, 2013). Skeletal muscle is around 75% water, indicating that those who have more muscle mass have a higher proportion of water in their body (Marieb & Hoehn, 2013).
Benefits of Consumption
Water is essential as building material in DNA, extracellular components, intracellular components, and proteins; it acts as a solvent for ionic compounds and other solutes; it provides a medium for chemical reactions within the body, often participating in the reactions; it carries nutrients and oxygen to cells; it carries waste products out of the cells and body; it aids in maintaining a constant body temperature; it lubricates and moistens tissues in the eyes, joints, mouth, mucus membranes, nose, and skin; and it acts as a shock absorber to help keep the structural integrity of cells and connective tissues (Gale, 2014; Pizzorno & Murray, 2013).
Many body structures require large amounts of fluid. For instance, it is estimated that we swallow around 1 L of saliva daily, and produce 200 mL of colon fluid secretions, 1 L of bile, 1.5 L of gastric fluids, and 2 L of intestinal juices (Campbell, 2003). Urine, produced in the kidneys, is a result of filtering around 1.2 L of blood per minute to remove toxic wastes from metabolic processes, such as urea and creatine, as well as certain drugs, potassium, sodium, water, and water-soluble vitamins like B vitamins and vitamin C (Campbell, 2003). Urine is 95% water and 5% solutes, and healthy adults produce 1 to 2 L of urine per day (Campbell, 2003).
Water intake is driven by the thirst mechanism, which uses osmoreceptors in the extracellular fluid to detect a gain or loss in water (Marieb & Hoehn, 2013). This in turn causes dry mouth, or a decrease in production of saliva, and a decrease in blood pressure, both of which trigger the body to feel thirst (Marieb & Hoehn, 2013). When thirst is quenched by drinking water, a signal is sent to the osmoreceptors that there is enough water in the body (Marieb & Hoehn, 2013). Thirst is not always a reliable indicator, particularly in athletes, older adults, or people suffering from renal or cardiac conditions, where the thirst mechanisms are not as sensitive, and may not activate the triggers of thirst even when they body is dehydrated (Marieb & Hoehn, 2013). When thirst is not quenched, it can lead to dehydration.
Signs of dehydration include dark and concentrated urine, dry mucous membranes, dry skin, constipation, fatigue, headache, irritability, low blood pressure, nausea, nosebleed, shallow, rapid breathing, and weakness, among others (Pizzorno & Murray, 2013). Water is lost from the body through perspiration, in urine, through respiration, and through feces (Pizzorno & Murray, 2013).
Athletes and older adults are particularly susceptible to dehydration. When dehydrated, “athletes may experience problems such as cramps, delirium, vomiting, hypothermia, and hyperthermia” (Schlenker & Roth, 2011, p. 323). To prevent this, athletes should be properly hydrated before exercising, and replace fluids during and after exercise (Schlenker & Roth, 2011). It is important to watch the water consumption in older adults. Often, the elderly do not drink enough water because they are not sensitive to having dry mouth, and they want to avoid incontinence problems, which can lead to “dehydration, constipation, cardiovascular disease, and deep-vein thrombosis/pulmonary embolism” (Tsuboyama-Kasaoka & Purba, 2014, p. 505).
Not only is water vital for maintaining life and health, but appropriate consumption of water can be therapeutic in treating arthritis, chronic fatigue syndrome, colitis, constipation, coronary heart disease, edema, fibromyalgia, hangover headaches, hypertension, intermittent claudication, low back pain, migraines, obesity, and peptic ulcers (Pizzorno & Murray, 2013). Water consumption helps to minimize the risk of developing kidney stones (Gale, 2014).
Research showed that not drinking enough water was as harmful to heart health as smoking. Drinking more water reduced the risk of heart attack deaths by 50% (Pizzorno & Murray, 2013). A study found that men who drank five or more glasses of pure water daily, only had 46% risk of fatal heart attack when compared to men who drank two or less glasses of pure water daily. In women, the risk was 59%. Conversely, women who drank five or more glasses of fluids other than pure water, including juices, soft drinks, tea, and others, had 147% greater risk of a heart attack than those who consumed two or less glasses of other fluids. In men, the risk was greater by 46% (Pizzorno & Murray, 2013).
Other evidence indicated that exercise-induced asthma is caused from dehydration of mucous membranes occurring even before exercise begins (Pizzorno & Murray, 2013). Thus, it is important for those with exercise-induced asthma to be properly hydrated prior to starting an exercise routine (Pizzorno & Murray, 2013).
The absolute minimum requirement of water for a person is 7.5 to 15 L of water per day to cover their needs for consumption (2.5 to 3 L), basic hygiene (2 to 6 L), and cooking (3 to 6 L) (Tsuboyama-Kasaoka & Purba, 2014). The minimal consumption of water for a normal adult is 700 to 800 mL to make up for water losses and maintain water balance (Gale, 2014). However, to ensure proper health, it is advised to consume 1.4 to 2.0 L of water per day (Gale, 2014). The specific amount of water varies by a person’s age, environment, exertion, and size. Water intake needs to increase with exercise, in hotter and more humid climates, in higher altitudes, when taking prescription drugs, to aid in dieting, when traveling, in an environment where air is recirculated, and when there is illness (Gale, 2014). Infants require 0.7 L of water, children require 1.3 to 1.7 L, teenage males require 2.4 to 3.3 L, teenage females require 2.1 to 2.3 L, adult men require around 3.7 L, adult women around 2.7 L, pregnant women around 3 L, and lactating women around 3.8 L of water daily (Pizzorno & Murray, 2013). However, adjustments are needed for those suffering from disorders, people consuming high amounts of protein, and people taking diuretics (Pizzorno & Murray, 2013).
Excessive water intake can occur when an adult consumes more than 7.6 L of water per day, as this can lead to hyper-hydration, where the body is unable to excrete excess water (Gale, 2014). Symptoms include confusion, disorientation, muscle cramps, nausea, and slurred speech, and can lead to death (Gale, 2014).
Typically 70 to 80% of water intake can come from water, juices, teas, and other drinks, and 20 to 30% of water can come from foods with high water content, such as fruits and vegetables (Pizzorno & Murray, 2013).
Campbell, J. (2003). Campbell’s Physiology Notes for Nurses. London, England: Whurr Publishers Ltd.
Gale (2014). The Gale Encyclopedia of Alternative Medicine, (4th Ed). Farmington Hilla, MI: Gale Cengage Learning.
Marieb, E.T. & Hoehn, K. (2013). Human Anatomy & Physiology (9th ed.). Glenview, IL: Pearson Education.
Pizzorno, J. E. & Murray, M. T. (2013). Textbook of Natural Medicine (4th ed.). St. Louis, MO: Churchill Livingstone.
Schlenker, E. D. & Roth, S. L. (2011). Williams’ Essentials of Nutrition and Diet Therapy- Revised Reprint (10th ed.). St. Louis, MO: Elsevier Mosby.
Tsuboyama-Kasaoka, N. & Purba, M. B. (2014). Nutrition and earthquakes: experience and recommendations. Asia Pacific Journal of Clinical Nutrition, 23(4), 505-513. doi:10.6133/apjcn.2014.23.4.23