The Institute of Medicine recommend that men achieve a daily fluid intake of around 3 liters and that women take in 2.2 liters.
Around of 70% of the body is comprised of water, and around of 71% of the planet's surface is covered by water. Perhaps it is the ubiquitous nature of water that means that drinking enough of it each day is not at the top of many people's lists of healthy priorities?
One part of the body that relies on adequate water intake is the kidneys. The kidneys are organs that might not get as much attention as the heart or lungs, but they are responsible for many functions that help keep the body as healthy as possible.
But what happens to the kidneys when we do not drink enough water? And what can be done to improve our levels of hydration? On World Kidney Day, we take a look at the role of drinking enough water for two of the most important organs in the body.
Why do we need to drink water?
Water is needed by all the cells and organs in the body in order for them to function properly. It is also used to lubricate the joints, protect the spinal cord and other sensitive tissues, regulate body temperature and assist the passage of food through the intestines.
Although some of the water required by the body is obtained through foods with a high water content - soups, tomatoes, oranges - the majority is gained through drinking water and other beverages.
During normal everyday functioning, water is lost by the body, and this needs to be replaced. It is noticeable that we lose water through activities such as sweating and urination, but water is even lost when breathing.
Drinking water, be it from the tap or a bottle, is the best source of fluid for the body. Beverages such as milk and juices are also decent sources of water, but beverages containing alcohol and caffeine, such as soft drinks, coffee and beer, are less than ideal due to having diuretic properties, meaning that they cause the body to release water.
How much water should you drink?
The recommended amount of water that should be drunk per day varies from person to person depending on factors such as how active they are and how much they sweat. There is no universally agreed upon threshold of water consumption that must be reached, but there is a general level of consensus as to what a healthy amount is.
According to the Institute of Medicine (IOM), an adequate intake for men is approximately 13 cups (3 liters) a day. For women, an adequate intake is around 9 cups (2.2 liters).
Many people may have heard the phrase, "Drink eight 8-ounce glasses of water a day," which works out at around 1.9 liters and is close to the IOM's recommendation for women. Drinking "8 by 8" is an easy-to-remember amount that can put people on the right track in terms of water consumption.
Water also helps dissolve minerals and nutrients so that they are more accessible to the body, as well as helping transport waste products out of the body. It is these two functions that make water so vital to the kidneys.
Learn more about how much water we should drink each day, including information about how the body regulates water and dietary sources of water intake.
What do the kidneys do?
The kidneys are two small fist-sized organs that are shaped like beans. They are located in the middle of the back, on either side of the spine and situated just below the rib cage.
Despite their importance, the kidneys can sometimes receive less attention than other organs in the body. "The role of the kidneys is often underrated when we think about our health," state Kidney Health Australia.
The role of the kidneys in keeping the body healthy may be underrated in relation to the heart and the lungs.
"In fact, the kidneys play an important role in the daily workings of our body. They are so important to health that nature gave us two kidneys to cover the possibility that one might be lost to an injury. They are so important that with no kidney function, death occurs within a few days."
A crucial function of the kidneys is to remove waste products and excess fluid from the body via urine. The kidneys also regulate the levels of salt, potassium and acid in the body and produce hormones that influence the performance of other organs.
When we eat and drink, nutrients and minerals enter the bloodstream in order to be transported around the body and used for energy, growth, maintenance or repair. The blood also passes through the kidneys where it is filtered, and any waste products and excess nutrients and water are removed and sent to the bladder for expulsion.
Every day, the kidneys filter around 200 quarts of fluid. Of these, approximately 2 quarts are removed from the body in the form of urine, and 198 are recovered by the bloodstream.
If the kidneys do not function properly through kidney disease, waste products and excess fluid can build up inside the body. Untreated, chronic kidney disease can lead to kidney failure, whereby the organs stop working, and either dialysis or kidney transplantation is required.
Water is important for the workings of the kidneys, not only for helping to initially dissolve the nutrients, but for ensuring that waste products, bacteria and proteins do not build up in the kidneys and the bladder. These can lead to dangerous infections and painful kidney stones.
How does not drinking enough affect the kidneys?
Urinary tract infections (UTIs) are the second most common type of infection in the body and account for around 8.1 million visits to health care providers in the US every year. If infections spread to the upper urinary tract, including the kidneys, permanent damage can be caused. Sudden kidney infections (acute) can be life-threatening, particularly if septicemia occurs.
Drinking plenty of water is one of the simplest ways to reduce the risk of developing a UTI and is also advised for people that have developed an infection.
The presence of kidney stones can complicate UTIs as they can compromise how the kidneys work. Complicated UTIs tend to require longer periods of antibiotics to treat them, typically lasting between 7 and 14 days.
The leading cause of kidney stones is a lack of water, and they are commonly reported in people that have been found not drinking the recommended daily amount of water. As well as complicating UTIs, research has suggested that kidney stones also increase the risk of chronic kidney disease developing.
In November 2014, the American College of Physicians issued new guidelines for people who have previously developed kidney stones, stating that increasing fluid intake to enable 2 liters of urination a day could decrease the risk of stone recurrence by at least half with no side effects.
Dehydration - using and losing more water than the body takes in - can also lead to an imbalance in the body's electrolytes. Electrolytes, such as potassium, phosphate and sodium, help carry electrical signals between cells. The levels of electrolytes in the body are kept stable by properly functioning kidneys.
When the kidneys are unable to maintain a balance in the levels of electrolytes, these electrical signals become mixed up, which can lead to seizures, involving involuntary muscle movements and loss of consciousness.
In severe cases, dehydration can also lead to kidney failure, a potentially life-threatening outcome. Possible complications of chronic kidney failure include anemia, damage to the central nervous system, heart failure and a compromised immune system.
There are a considerable number of health problems that can occur simply through not drinking enough water, and yet researchers have found that a significant number of Americans may be failing to obtain the recommended levels of fluid intake every day.
Does the US not drink enough water?
A study carried out by the Centers for Disease Control and Prevention (CDC) in 2013 analyzed data from the National Cancer Institute's 2007 Food Attitudes and Behaviors Survey, in order to assess the characteristics of people who have a low intake of drinking water.
A recent study conducted by the CDC suggested that many people in the US may not be drinking enough water.
Out of a sample of 3,397 adults, the researchers found the following:
- 7% of adults reported no daily consumption of drinking water
- 36% of adults reported drinking 1-3 cups of drinking water a day
- 35% of adults reported drinking 4-7 cups of drinking water a day
- 22% of adults reported drinking 8 cups or more a day.
People were more likely to drink less than 4 cups of drinking water daily if they consumed 1 cup or less of fruits or vegetables a day. The study indicates that among this sample, a large number of people may well have not been drinking the suggested 8 cups of fluid a day.
Although the study only measured the intake of drinking water and fluid can be gained from other beverages, water is the ideal source of fluid due to it being readily available, calorie-free, caffeine-free and alcohol-free.
The fact that 7% of respondents reported drinking no water at all daily, and that respondents who drank low volumes of water were associated with low levels of fruit and vegetable consumption, would suggest there is a certain number of people who are risking their health by not getting enough fluid.
Even if the respondents reporting low levels of water intake were obtaining enough fluid, it is likely that they would be obtaining it from sources that could potentially compromise their health in other ways.
"The biologic requirement for water may be met with plain water or via foods and other beverages," write the study authors. "Results from previous epidemiologic studies indicate that water intake may be inversely related to volume of calorically sweetened beverages and other fluid intake."
The CDC make a number of suggestions that could help people increase the amount of water they normally drink:
- Carrying a water bottle with you means that fluid can be accessed when out and about, at work or running errands
- This water can be frozen in freezer-safe water bottles to provide a supply of ice-cold water all day long, which can be more satisfying than other beverages in certain situations
- Adding a wedge of lime or lemon to water can give it a different edge that may improve its taste without affecting its nutritional value.
Drinking enough should be an easily achievable health goal. "Under normal conditions, most people can drink enough fluids to meet their water needs," state the CDC. Although it is a relatively simple step to take, it can easily get overlooked as part of increasingly hectic lifestyles.
On National Kidney Day, it is worth remembering the risks that can come from not getting enough fluids, and to raise a glass - ideally filled with water - to those underrated organs that do so much for the health of the body.