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How Much Water Are You Supposed To Drink? Your Urine Will Tell You

Perhaps you’ve heard that increasing your water intake is part of a healthy lifestyle – and that you should drink at least 8 glasses of a day. This “rule of thumb” is actually not based on scientific evidence. Although for many people it’s not harmful advice, you may not need to work so hard at getting enough water every day.

The amount of water that your body needs depends on three main variables (yes, needs can vary with different illnesses and conditions, but let’s talk about the average American):

1. Your body’s size

2. Your activity level

3. Your environment (weather and humidity conditions)

The larger you are, the more water you lose from sweat (be it from physical activity or hot weather conditions), the more water you need to replace. The amount you need can vary a lot – and in most cases there are two tricks you can use to stay properly hydrated:

1. Drink when you’re thirsty

2. Drink enough water to keep your urine a light yellow or clear color

Now, in extreme cases where you’re exercising very vigorously for long periods of time, or are in hot, dry environments (such as the desert southwest) sometimes your thirst feeling is activated too late – and you’re already dangerously dehydrated by the time you feel like drinking. If you’re going to be in these situations, then it’s important to calculate your hydration needs in advance (including electrolyte replacement), and bring enough fluids with you. There is a nifty hydration calculator online here.

For those of you who are curious to see approximately how much water your body needs per day, you might also want to play with the hydration calculator. Keep in mind that it suggests your total daily hydration requirements in cups, and that we already get a significant amount of fluid through what we eat.

Imagine your morning cereal with orange juice for example.  The cup of milk you used is basically a cup of water (with other nutrients in it) and so is the juice. So in the end, you don’t need to think of the suggested number of cups/day as additional glasses of pure water that you must drink. I know a lot of people who try to force down extra glasses of water when they’re not thirsty, assuming that it’s the healthy thing to do.

Believe it or not, some people have died from drinking too much water. This is quite hard to do – drink yourself to death – but it illustrates that it’s important to be balanced in your hydration efforts. Too little water is bad, but so is too much! The good news is that in most cases, your body’s thirst mechanism will tell you what you need. And if you want to double-check that you’re getting enough fluids, a quick look at your urine will tell you just about all you need to know.

Why is that? Because your body gets rid of extra fluid that it doesn’t need via the kidneys. The kidneys filter excess fluid (and other substances) out of the bloodstream and make urine out of it. When the urine is dark yellow, it means that the kidneys didn’t need to remove much water – they’re holding on to the water because they sense the body is relatively dry. When the urine is light yellow or clear, the kidneys are dumping the extra fluid into the urine (diluting the substances) because they know your body is sufficiently hydrated.

So there you have it! If you’re one of those people who have been feeling guilty about not getting enough water every day, maybe your body doesn’t need it? Check in with your urine to get the final answer.

(In case you didn’t know what the image above has to do with this blog post, it’s a screen image from the 1995 movie, Waterworld. There is a scene where Kevin Costner drinks his own urine… which could be the reason why the movie was one of the most expensive flops in Hollywood history?)

P.S. For those of you following along with the Boys & Girls Clubs’ Triple Play Fit Family Challenge, this post is part of a series of nutrition tips that I’m offering the families over the next 6 weeks. You can read my tips from the beginning:

1. Healthy Eating: It All Boils Down To 3 Pieces Of Advice

2. Seven Secrets To Successful, Long Term Weight Loss

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2 Responses to “How Much Water Are You Supposed To Drink? Your Urine Will Tell You”

  1. Ben says:

    Thank you! It’s always bugged me that this arbitrary piece of advice has had so much sticking power. The “Drink when you’re thirsty” is almost certainly the key to proper hydration (except in cases of some illnesses and extreme physical feats) and if your urine is reasonably colored you’re probably getting a decent supply of water. Docs tend to be ambivalent (“it can’t do any harm”), but there are real consequences to the public perception that you need to be drinking at every moment: American’s water habit is expensive both monetarily and environmentally: the growth of the bottled water industry has capitalized on (and promoted) this apocryphal medical wisdom at the cost of consumers and the a substantial amount of litter, plastic manufacturing, and transportation costs. Never mind that large numbers of real maladies are attributed to “not getting enough water”.

    Even in cases when old-wives-tales are truly harmless, science-based medicine has a responsibility to not be seen as tacitly endorsing views that are not supported by evidence. We don’t need an anti-water crusade, but docs should probably at least put the message out there that this is junk science.

  2. Cynthia Bailey MD, Dermatologist says:

    This is a great and practical explanation for a subject that’s totally lost in myth. It’s also a subject that health proponents take firm stands on, all without evidence. In particular, I love that 8 glasses a day recommendation without the inclusion of other beverages consumed, activities engaged in, or each person’s unique metabolic issues.

    I exercise a lot and my water and salt need have varied over the years. I could never just follow the 8 glasses a day admonition as my guide. When I was younger I used to sweat profusely with exercise and the sweat was very minerally. I needed a lot of water daily and a surprising amount of salt with my food too. Now that I’m older my body seems to sweat less with exertion (it now sweats mostly from hot flashes which have a mostly watery sweat oddly), and I seem to need less salt. When I was younger, just drinking water without increasing salt intake would result in being light headed with exercise. Now that I’m older it’s fine. I’ve always watch the color of my urine and how I feel during sweat inducing exercise, and use that to gauge my daily water (and for me salt) need. I watch my blood pressure for confirmation that I’m staying in a healthy range. It works well. I drink water, juiced veggie juice and tea all day long and never need to count total volume or push myself to consume more.

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