Water is essential to life. It is a macronutrient required by the body in large amounts each day, although it cannot be stored by the body. Water helps with many bodily functions and is lost daily from the body through functions such as urinating, sweating and breathing. This lost water needs to be regularly replaced.

The appropriate amount of water needed each day may depend on a number of factors, such as age, gender, body composition (amount of lean muscle versus fat tissue) and level of physical activity. Drinking water is the best way to give the body what it needs. Other beverages and foods are important sources of water as well.

Most people get their water from a public drinking water source. It is disinfected and treated to remove detected contaminants that exceed acceptable levels established by the U.S. Environmental Protection Agency (EPA). Some people rely on water from private wells, which are not regulated by the EPA, although most state and local governments have laws that govern the safety of water from private wells.

Bottled water has become increasingly popular. There are many different types of bottled water. Some have been minimally treated to remove possible contaminants, others may have been treated in such a way to eliminate bacteria and viruses. Bottled water is regulated by the U.S. Food and Drug Administration.

Water filters may be used by consumers at home to help remove certain contaminants that may be present in tap water. There are several different types of filters, although no one filter can eliminate or reduce all possible contaminants. Water softeners are sometimes used to reduce the level of hard minerals (e.g., calcium, magnesium) in water. Soft water makes soap lather better and helps dissolve contaminants that may come from old plumbing pipes.  

Water is a colorless, tasteless, odorless substance essential to all known forms of life. It is formed by a combination of two parts hydrogen and one part oxygen (H₂0). Water is the nutrient required in the largest amount by our bodies, more than carbohydrates, protein, vitamins or minerals. Water is considered a macronutrient because it is essential in large amounts each day. However, it cannot be stored in the body like other nutrients. Daily replenishment of water is necessary to maintain body function and to avoid dehydration (the excess loss of water and electrolytes).

The body is made up of approximately 60 percent water. Water composition depends on factors such as age, gender and body composition (amount of lean muscle versus fat tissue). Muscle holds more water compared to body fat. Infants’ and children’s bodies have a higher percentage of water. On average, females, the elderly and obese people have less water in their bodies.

A majority of the water in the body is found inside body cells (intracellular fluid). The remaining amount is known as extracellular fluid. This water outside the cells helps to make the blood and bodily secretions (e.g., saliva, tears, urine). This extracellular fluid carries electrolytes and can move in and out of the semi-permeable membranes of body cells (a process known as osmosis).

If fluid imbalances occur, the body automatically responds to restore the balance. For example, if there is too much of a mineral (e.g., sodium) inside the cell and not enough fluid, the body will send water inside the cell to restore the proper balance. It can also send water outside the cell if there is too much fluid and too little of a mineral inside. The body continually makes quick, automatic adjustments to achieve a balance of fluids inside and outside body cells. The natural tendency of the body to maintain stability in such a way is called homeostasis.

Water is essential to life because it:

• Regulates body temperature through perspiration
  
  
• Helps the body absorb nutrients and convert food into energy
  
  
• Transports nutrients and oxygen to cells
  
  
• Helps to moisten body tissues (e.g., in the mouth, eyes, nose and throat)
  
  
• Lubricates joints and protects body organs
  
  
• Helps to prevent constipation by softening stool
  
  
• Helps carry waste out of the body
  
  
• Is the main component in every body fluid (e.g., blood, gastric juices, urine, saliva, amniotic fluid for a developing infant)

A person cannot survive for long without drinking water. Although people can survive for several weeks without consuming any food, they cannot live more than a few days without water.

The National Academy of Science’s Food and Nutrition Board defines the daily adequate intake levels of water (from beverages and food) for healthy adults as:

• 2.7 liters (about 11 cups or 91 ounces) for women
  
  
• 3.7 liters (about 16 cups or 125 ounces) for men

Most experts agree that a good rule of thumb is to drink at least eight 8-ounce glasses of water a day. However, individual hydration needs vary. Most healthy adults need about 1 to 1.5 liters of water per 1,000 calories of energy they consume. Thus, people who consume 2,000 calories per day will need approximately 8 cups of water (about 2 liters) per day.

People get most of their water needs met through drinking, which constitutes about 80 percent of a person’s total fluid intake. Drinking water is the easiest way to get adequate quantities each day. Other beverages are a good source of water (e.g., juice, milk, tea, soda), although they may also include substances that encourage water loss. For example, the caffeine commonly found in coffee, tea and soft drinks acts as a diuretic, increasing the amount of fluid expelled from the body in urine.

Food also contains water and is usually responsible for about 20 percent of a person’s total fluid intake. Many fruits, vegetables, meat and legumes derive more than half of their weight from water. Foods with an extremely high water content include Iceberg lettuce, watermelon, cucumbers, broccoli, squash, grapefruit and oranges. Even so-called dry foods have some water content (e.g., bread, nuts). Oils do not contain any water.

In addition to water supplied by the diet, a small amount of the body’s water is produced inside body cells. This occurs during the body processes of digestion and metabolism.

Waiting to drink until the sensation of thirst appears is not a good indicator of proper hydration. Thirst is actually a symptom of mild dehydration. People who are well hydrated are rarely thirsty, and have urine that is colorless or only slightly yellow.

On average, adults lose approximately 10 cups (2.4 liters) of water each day, which must be replaced. Reasons for water loss in healthy adults include:

• Urine. This is the greatest source of water loss, with about 4 to 6 cups (0.95 to 1.42 liters) daily. If more or less water is taken in it can change the amount of urine excreted.
  
  
• Sweat. Perspiration accounts for about 2 to 4 cups (0.47 to 0.95 liters) of water lost per day. Variations in this amount depend on factors such as heat, humidity and level of physical activity.
  
  
• Breathing out (exhalation). This is known as insensible water loss because people are essentially unaware of this process. Breathing can result in the loss of about 1.5 cups (0.35 liters) of water per day.
  
  
• Stool output. Bowel movements account for the loss of approximately two-thirds of a cup (0.16 liters) of water each day. When a person has diarrhea, this amount significantly increases.

Vomiting is also responsible for fluid loss. It may occur during certain illnesses or in people with certain conditions (e.g., bulimia nervosa). When it occurs, vomiting can account for a significant loss of fluids.

No tolerable upper intake levels have been established for water. Most people do not drink excessive amounts of water, and healthy kidneys can usually handle more than 24 ounces of fluid per hour. However, a rare condition called dilutional hyponatremia (inadequate sodium levels due to excess extracellular fluid) may occur when people drink too much water. When water moves into body cells to achieve fluid balance, the cells may begin to swell. Most cells can handle extra water, but brain cells cannot because the brain is confined by the skull. Swelling of the brain is a life-threatening complication of this condition.

Public drinking water is obtained from surface water, which may be found in rivers, lakes and reservoirs. It is easily contaminated due to acid rain, highway runoff, pesticides, dumping of industrial wastes, as well as human and animal wastes. This contamination can be reversed with fresh rain, aeration, sunlight and certain plants and microorganisms found in the water.

Public drinking water is disinfected and treated to remove detected contaminants when they exceed acceptable levels established by the Environmental Protection Agency (EPA). The most common disinfection method is the addition of chlorine to the water supply. Chlorine kills fecal bacteria that may cause life-threatening waterborne diseases (e.g., cholera, dysentery, typhoid fever). These are no longer a public health threat in the United States due to chlorine disinfection. Another disinfectant method is the use of ultraviolet light to kill harmful microorganisms.

Municipal water suppliers provide an annual water quality report called the Consumer Confidence Report. It includes the following information:

• Quality of the drinking water in the past calendar year
• Source of the water
• Levels and suspected sources of contaminants
• Maximum contaminant levels
• Treatments used

Well water (groundwater) is found in aquifers and pumped to the surface. Contamination is difficult, but can occur due to seepage from hazardous waste sites, landfills, dumps, underground gasoline and chemical tanks, or improperly disposed of household chemicals and solvents. Well water does not receive the benefit of the sun, air or aerobic organisms that may help neutralize certain types of water contamination. Well owners are advised to annually test the quality of their water.

According to the EPA, approximately 15 percent of people in the United States use private drinking water wells. The EPA does not regulate the quality of water from these sources, but most state and local governments have laws that govern the safety of water from private wells.

Many people choose to drink bottled water instead of public drinking water. For many people this is because of:

• Taste considerations. When people say their water has a taste, what they taste are the minerals that may be in their tap water. Minerals that naturally occur in water include magnesium, calcium, sodium, copper, fluoride, iron and uranium. Certain types of bottled water remove these minerals from the water, leaving it with no taste.
  
  
• Perception that bottled water is better than tap water.
  
  
• Health considerations. Certain people may be susceptible to particular contaminants in public drinking water. This may include children or anyone with a weakened immune system (e.g., due to chemotherapy, HIV/AIDS, Crohn’s disease, lupus, organ transplant). These people may choose to use bottled water instead of public drinking water.  

Bottled water costs more than public water. Consumers may want to factor in financial cost when considering whether to drink bottled water, filtered tap water, unfiltered tap water or a combination of these.

Bottled water is regulated by the Food and Drug Administration (FDA) under the Federal Food, Drug and Cosmetic Act. Bottled water must follow processing, packaging, shipping and storage rules for safety and sanitation. It must be truthfully labeled and meet FDA standards of contaminant levels, which are set by the Environmental Protection Agency (EPA). States may have additional regulations for bottled water sold within their borders.

Bottled water does not usually contain chlorine, but it may if it is bottled from a public drinking water source. Sweeteners are prohibited in bottled water. Additives, such as flavors, extracts or essences from food or spices, cannot exceed 1 percent by weight. Some beverages appear to be a type of water but are not considered water by the FDA. These include tonic water, sparkling water, seltzer water, soda water and club soda. These products are considered soft drinks.

Bottled water may have different names, depending upon its source, how it is obtained and processed, and whether it contains additives. The FDA does not regulate bottled water sold outside the United States.

The FDA prohibits health or medical claims about bottled water. Bottled water has not been proven useful for therapeutic purposes.

Water filters may be able to remove certain contaminants from tap water, but cannot effectively eliminate all viruses or bacteria. Filters must be replaced regularly and according to the manufacturer’s directions. Without proper maintenance, bacteria can build up in the filtration products and contaminate drinking water. Point-of-use filters are installed on household water faucets. Point-of-entry filters are installed where the water line enters the house to treat water being used throughout the house.

There are several different types of water filters. No one filter can eliminate or reduce all possible contaminants. Common types of filters include:

Water may be characterized as hard or soft, depending upon its mineral content. Hard water is high in calcium and magnesium, which has been dissolved from soil and rainwater. Soft water has greater amounts of naturally occurring sodium and potassium.

Fluoride is a mineral that appears naturally in soil, water, air and certain foods. It is often added to public drinking water to help prevent tooth decay and is considered a cost-effective method of delivering fluoride to all members of the community. The Centers for Disease Control and Prevention (CDC) recommends drinking fluoridated water along with using fluoride products (e.g., fluoride toothpaste) on a regular basis as part of good dental hygiene.

Fluoride was first added to community drinking water in the United States in 1945. Studies of its effects over a 15-year period found that fluoridated water reduced tooth decay in children by 60 percent. According to the CDC, as of December 31, 2000, almost 66 percent of the United States population receives public drinking water that is fluoridated.

The optimal range for fluoride levels in drinking water is between 0.7 (for warmer climates) and 1.2 (for cooler climates) parts per million (ppm) or milligrams per liter, according to the U.S. Public Health Service. Drinking water with levels of fluoride above 2 ppm may cause dental fluorosis in children. This may be more likely to occur in communities that do not regulate fluoride levels in the water, or among those who rely on well water with naturally occurring high levels of fluoride. Community water that is fluoridated is monitored daily to ensure that proper levels of fluoride are maintained.

Most people support water fluoridation. However, people who oppose it have questioned its safety and argued that it is a decision imposed upon them by others.

Preparing questions in advance can help patients to have more meaningful discussions with health professionals. Patients may wish to ask their doctor or registered dietitian the following questions related to water:

1. How much water should I drink every day?
   
   
2. Can I get this daily amount from other fluids besides water? What types of beverages do you recommend?
   
   
3. Do you recommend the local tap water? Why or why not?
   
   
4. What are the benefits and risks of fluoridated water? Do you recommend I drink it?
   
   
5. Do you recommend I use a water filter? What type?
   
   
6. Do you recommend I consume bottled water? Why or why not?
   
   
7. Are there specific types of bottled water you recommend?
   
   
8. How can a water softener affect my health?
   
   
9. How can I check the quality of water from a private well?
   
   
10. How will I know I am getting enough water?
    
    
11. Are there any risks associated with drinking too much water?