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How much fluid should a person take in on a given day?

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By Steve Prentice | Last updated: February 12, 2021

How can a person determine how much fluid they should take in on a given day?

The human body is between 60% to 75% water, and every part of the body – including organs, blood, bones, brain, eyes, and skin – needs water to function. It can be thought of as both a building block and a fuel.

One of the ways to determine fluid amount needed is by percentage. Going just 15% below your required fluid levels can start a dangerous slide towards death. Vital fluids not only support organ function, they also assist in the delivery of nutrients, the excretion of poisons and wastes, and the maintenance of body temperature. Once you stop taking fluids in, the body starts to shut down. Symptoms include dizziness, headache, and disorientation, followed by weak pulse, cardiac problems, and then organ failure. Death can occur directly from dehydration or indirectly from cardiac issues or errors/accidents made through disorientation. It only takes three days of absolutely no fluid intake for death to occur.

(Learn more in Disorientation, Dizziness, Loss of Consciousness: The Dangers of On-the-Job Dehydration.)

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Another way to determine how much fluid to take in is by amount. Most health specialists still stick with the metric of “the equivalent of eight glasses of water a day.” Many foods contain liquid within them. Fresh fruits like apples and grapes can be between 65% and 90% water. A good habit is to always have a water source at hand and to take from it regularly, such as sips of water or a fresh fruit snack. It’s also important to remember that beverages like coffee and tea, even though they are fluids, contain caffeine, which is a diuretic, meaning it triggers expulsion (urination) more quickly. So, if you drink coffee (even decaf), you should add one extra glass of water to balance it out.

Working conditions have a big impact on fluid requirements. Hot environments will elicit perspiration and both humid and dry air dehydrate the body. Intense physical labor generates thirst more quickly by burning calories and increased exhalation, but even sedentary work at a desk in an office demands close attention to hydration, especially when coffee and tea, sugary soft drinks, and salty foods are included.

(Learn more in It's Not All About Fluids: 5 Factors That Can Lead to Dehydration.)

Humans need regular hydration every day, regardless of gender, age or background. Even when you do not feel thirsty, regular water intake every 15 to 20 minutes is vital. In fact, you should never wait until you feel thirsty, you should try to always avoid that sensation. Prehydrating should start a few hours before activity starts in order to enable fluid absorption and allow urine output to maintain normal levels.

A note on sports drinks. Some sports drinks help with electrolyte replacement, which is a good thing during prolonged exertion. However, they vary in terms of their sugar content, which can further tax the body’s recovery through the presence of sugars such as fructose. Consuming water, as well as foods that have a high water content, such as fresh fruits and vegetables, is a better course of action. In some working conditions, electrolyte-rich drinks are important to hydration. If sugar is still a concern, there are low-sugar and sugar-free electrolyte beverages on the market.

(Read about Electrolytes: What They Are and Why They Matter for On-the-Job Hydration.)

There's no easy answer to how much fluid a person should take in a given day, but the safest bet is to simply take a few sips of water every 15 to 20 minutes.

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Written by Steve Prentice

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Steve Prentice is a project manager and a specialist in productivity and technology in the workplace. Much of his work focuses on techniques for creating and maintaining safe and healthy working environments. He believes new educational technologies will go a long way in establishing policies and practice that support safe and balanced work, while blockchain tech will assist greatly in the process, and he assists companies in adopting these as new best practices. He is a published author of three self-help books, and is in high demand as a guest speaker and media commentator. His academic background is in organizational psychology and project management.

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