Doctor's Note

More on children and hydration:
Does a Drink Of Water Make Children Smarter?

And check out my other videos on beverages

For more context, check out my associated blog post: Schoolchildren Should Drink More Water.

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  • Michael Greger M.D.

    Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on beverages. Also, there are 1,449 other subjects covered in the rest of my videos–please feel free to explore them as well!

  • how does distilled water rate compared to bottled water and tap water?

    • NickyC

      Hi Trinda,

      Distilled water is water that has been turned into steam, leaving the impurities such as chlorine, lead, fluoride, washed up pharmaceuticals, and essentially everything else behind. The steam is then condensed to make pure water. This process also kills and removes bacteria, viruses – basically anything that is organic or inorganic. This water is a pure as it gets. While some people claim that the removal of minerals during this process is harmful, we actually get most of our minerals from the food we consume, and not water.
      Therefore, I believe that distilled water, by removing all impurities, is the safest water you can drink.

      • Ace Pex

        I’m sorry but this is completely wrong. While distilling water does remove all inorganic impurities, and kills organic pathogens (e.g., bacteria, viruses, etc), it does not remove all organic impurities. More specifically Volatile Organic Compounds (also known as VOCs) will vaporize just as the water does when it is boiled and come along for the ride when the steam is condensed back out into liquid water again. So unfortunately even distilled water can have lots of VOC contamination.

  • I have heard and read that the “only water that our bodies can actually use to clean their cells, is the water contained in vegetables” and that “bottled mineral water only serves to pollute the body, as the minerals have a low bio-availability and the body needs to work to remove them”.

    Then I am told in conferences that actually there are “studies that prove that bottled mineral water is good for you and that there are scientific studies proving this”, although nobody could actually produce any of these studies.

    I also hear that “tap water is polluted” and that with the “high amounts of pollutants, oestrogen, etc. it is best to avoid it”.

    I am then told that the “only water to drink is reverse osmosis”, as the “vegetables we eat will provide the water that the body needs for bodily functions” and the “extra water that is drunk – the reverse osmosis – will be pure and therefore not pollute the body, but will serve to lubricate the digestive system”.

    Then I read that reverse osmosis, being “empty and containing no minerals, will leach the minerals from the body creating deficiencies”.

    Another claim that I am now hearing is that we should drink “Kangen Water”, which apparently “alkalises your tap water” (although nobody says what it adds to do this or what is actually filtered from the water, i.e. pollutants, pesticides, etc.). It’s a filter system that you connect ot your tap water. The claim here is that “your body absorbs this alkaline water with miraculous effects”, even going as far to claim that it “can help cure some forms of cancer”. Nobody explains however how this water can pass through the acidity of the stomach and still end up alkalising the body when absorbed!

    There are probably other claims that I have heard and forgotten, but wondered if you have any information or have done any research here?

    Many thanks… Mark

    • Γ214

      Water naturally contains dissolved minerals. This is why well water and surface water taste so different (well water will generally have more minerals due to a longer time in the ground in order to dissolve them). These minerals are what makes water conductive. Pure water has a very high electrical resistance and is rather corrosive and has a very unpleasant taste to it.

      There are no published, reputable studies saying anything about negative effects from mineral water. This makes sense, as humans have been getting water from sources that have high mineral content (hard water, most people call it) since forever, seeing as how freshwater springs happen everywhere on Earth with few exceptions. The mineral content is re-added for the sake of taste, nothing else.

      We are also fine drinking rain water, which is for all intents and purposes, distilled water.

      Finally, the human body only operates within a very fine are of the pH scale. There is no evidence supporting alkalinizing or acidifying your body, and any action that would ACTUALLY be successful in doing so would cause severe illness and soon after, death.

  • Chelsea

    Mark Tucker: Tap water is highly regulated and tested for safety, whereas other sources are not. You can find water quality reports online from the Environmental Protection Agency if you’re in the US. From these reports (which can be found online), you can find what contaminants your tap water may contain, then simply look for a filter that works best for you in your area. From this, you can determine an in-home filtration device that will work best for you. The type of filtration is completely dependent on the quality of the water, so that should be the first step you take.

    As far as mineral content, whole foods are the best place to obtain minerals, vitamins, and all things necessary in your diet. There may be one supplement worth taking, however. See this video for more information:

  • Deemae

    What about the water in the U.K that’s fluoridated?

  • evanbrand

    What basic water filter do you recommend for daily drinking (does Pur pitchers do the trick?)?

  • evanbrand

    What shower filter(s) do you recommend (I am based in NYC and, like other US cities, the water supply has excessive chlorine, bromine, and fluorine).

  • evanbrand

    Is Poland spring water reputable?

  • papayoyo

    I heard recently that tap water is bad for health as the chlorine kills off the body’s beneficial bacteria.

    What about home filtered tap water or boiled mineral water?

    • Γ214

      In municipal drinking water supplies, the concentration is not high enough for any ill-effects.

      Chloride ions (which the chlorine dissociates into after entering solution with water) are necessary throughout the body. In nerve conduction they are what permits sodium, calcium, potassium, magnesium, and other ion channels to function, by pumping the ions across a barrier and releasing them when an electrical signal is needed. In the stomach, hydrogen chloride is the acid which performs the first primary step of food digestion. Again, in solution, that is just protons (H+ ions) and Chloride ions. The chlorine really has no ill-effects at normal tap-water levels.

  • ChrisH

    Chlorine, like fluoride, is an industrial toxin, and should be avoided. Tap water in some areas is full of it. All so-called natural spring, well, tap or mineral water, irrespective of whether filtered or boiled, will still contain anything, from (hopefully) lifeless bacteria and virus husks to inorganic metals, salts, minerals, trace elements etc. – pollutants all – turning every glass of water into a potentially life threatening cocktail. The powerful water lobby denies it, of course, and produces (or claims to possess) studies that offer scientific proof. I remain unconvinced – mainly because of scientific proof to the contrary (bone density comparisons between consumers in areas with very high and very low mineral content water, for example, where severe osteoporosis incidence was found to be almost double in the high mineral content water area). Not a paradox – the “enriched” water blocks absorption of organic (food) calcium, resulting in deficiency.
    In answer to your question, papayoyo, think H2O. That’s what your body cells want, nay, need. H2O, no toxic cocktails. Distilled water is almost 100% H2O. So is RO water. The latter has a waste factor, though, as it is said to take between 10 to 20 liters of tap water to produce a liter of RO water (depending on the device used, I guess).

  • papayoyo

    Thanks ChrisH for your informed reply. I’m inclined in the same direction of thought. Though what would you say to the argument that distilled and RO water leech minerals and nutrients from the body? Isn’t all life on the planet sustained by water that is infused with elements from the environment? Isn’t perfectly pure water an artificial and unnatural thing? I guess rain water is pretty pure but on it’s way down it must absorb “stuff” from the atmosphere.

    • ChrisH

      Thank you for that question, papayoyo.
      The bizarre notion of water maliciously leaching valuables from our organism (in the process leaving the infinitely more available – as no longer organically fused – waste materials, toxins, “ash”, etc., in the body cells) is persistently being bandied about by – I suspect – the water lobby (and maybe pension funds?).
      It has no scientific basis. The opposite is in fact true. Pure H2O enhances the efficiency of the metabolism, as H2O will readily transport nutrients through cell walls, and cleanse waste products from the cells in direct exchange.
      Rain is nature’s distilled water. The (mostly man-made) pollution it picks up in the atmosphere is in fact the “artificial and unnatural” thing. Being an efficient solvent, water begins breaking down whatever it encounters as soon as it hits the ground. For many simple organisms, amphibians, fish and practically all plants this fortified water is imperative to sustain life. Higher organisms generally can’t fully utilize the large molecular structure of inorganic minerals etc. and need to obtain the necessary from organic sources (food). Drinking the inorganically enriched (mineral, tap, well, spring) water will inevitably put strain on the organism, causing mineral deposits in joints, arteries, kidneys etc., contributing to arthritis, stroke, renal failure, arteriosclerosis etc., thus effectively reducing human life expectancy…

      • Moonchasis

        Your statements in the last paragraph are interesting. Can you please provide research and studies showing what you claim: 

          “Drinking the inorganically enriched (mineral, tap, well, spring) water will inevitably put strain on the organism, causing mineral deposits in joints, arteries, kidneys etc., contributing to arthritis, stroke, renal failure, arteriosclerosis etc., thus effectively reducing human life expectancy…”Thank you. This is very interesting but I do think it warrants documentation  to back it up.

      • Moonchasis

        thank you but please show who did this research. What study, and who were the authors of it?  Otherwise I am to assume that you are just making a theory based on what seems obvious to you. Surely you researched this and can provide the information on the study.

  • Moonchasis

    I can’t find a single study that claims that the minerals in mineral water are unhealthy for the human body. Can anyone provide some evidence of this?  I like natural mineral water but some people raise concerns so I am curious.

  • dharmarules

    Dear Dr. Greger, we are thinking of buying a water filtration system made with coconut shells that they say makes the water cleaner than any other system with no chemicals, if possible I would like your comments if you are familiar with this system, it’s the one with Ed Bagley advertising for it.Thank you for all you do !

  • Mark Hazell

    Should I bother filtering my water (with something like a brita)?

  • Derrek Hooyman
  • Rodrigo

    In my experience tap water drank regularly causes digestive problems. The overload of minerals overtaxes the system and lowers appetite, nutrients in food are not used adequately; when i drink tap water or any other brand of natural mineral water i could just keep eating and eating with no satisfaction (sugars probably get stuck in the bloodstream, maybe because of the overload) when i switch to purified water satiation comes way quicker and energy returns. I see this same effects on my dog. Also mineral waters take time to completely get out of the system, so it takes some time for the appetite and the adequate use of nutrients to return.

    The overload of minerals overtaxes the organs and sends me to a deep sleep in the afternoon.

    But mineral water also makes me feel happier and active during the day, so i think there should be a middle point, mineral water is very powerful so i just use it sparingly.

    I have no studies about this information this is just what i’ve observed.

    • Γ214

      Well water, here, very “hard”. No problems besides washing my hair (much worse at lathering the shampoo). Most surface-water supplies I’ve drunk from actually give me heartburn.

      If mineral water takes a while to get out of your system, where does it go? Do you actually have any understanding of kidney function and how it relates to rather quick elimination of excess minerals?

  • Andrea Mercier

    Good Morning Dr. Greger….I found this article which sounds like it was onboard for water consumption, but a few items in it…especially # 3 have me concerned…
    I follow and Dr. B and since switching to a WFPB diet in Sept 2014 the only thing I drink is water….well the occasional glass of red wine…but 99% water :)
    Can you please comment specifically on #1 where they say that all liquids count…I don’t believe drinking coffee and milk should count as water intake and # 3 about water and fiber creating blockages in the intestines… My belief is that if you don’t have an underlying health issue and drink water when you are thirsty and get a minimum of amount…(what is that?) you should be good to go.
    Thanks again for your videos…I believe them to be life saving!

    • Γ214

      You only need sufficient water to replace the water lost during the day in digestion, sweat, respiration, and urinary output. Drink enough to satisfy that and you are fine.

      Most folks have a proper feedback response for needing water and then feeling thirsty. Some do not for various reasons. 8 glasses a day is a suggestion for consuming more than adequate water to fulfill your needs. Your kidneys will see to eliminating the excess.

      Note: Dehydration is a risk factor of labor intensive work, hot climates, and GI illness. If one applies, you need to actively worry about dehydration, as well as sufficient electrolyte intake.

  • Stu

    I recently found information that has reversed my original position on the best water to drink and wanted to share.

    I found the following paper which in part states:

    “not only does completely demineralised water (distillate) have unsatisfactory organoleptic properities, but it also has a definite adverse influence on the animal and human organism”. After evaluating the available health, organoleptic, and other information, the team recommended that demineralised water contain 1.) a minimum level for dissolved salts (100 mg/L), bicarbonate ion (30 mg/L), and calcium (30 mg/L); 2.) an optimum level for total dissolved salts (250-500 mg/L for chloride-sulfate water and 250-500 mg/L for bicarbonate water); 3.) a maximum level for alkalinity (6.5 meq/l), sodium (200 mg/L), boron (0.5 mg/L), and bromine (0.01 mg/L).

    The lowest morbidity was associated with water having calcium levels of 30-90 mg/L, magnesium levels of 17-35 mg/L, and TDS of about 400 mg/L (for bicarbonate containing waters). The author concluded that such water could be considered as physiologically optimum.

    After finding the above information I set about searching for a water source that matches the WHO recommendation. Turns out there is a natural spring water source near me that is within the suggested parameters, bottled locally, and which the company performs and provides regular water analysis results. They ozonate, bottle (glass or polycarbonate) and have the water delivered to me within 72hours of collection.

    I am capable of modifying/making my water parameters match the recommendation, however, in my opinion it’s not practical to expect that an under the sink unit and a home kitchen based lab can do a better job at water handling than mother nature and a multimillion dollar water distribution company, the latter of which are subject to random testing and inspections by the Canadian government and the various certifying bodies to which they subscribe.

    I hope this helps someone. The .pdf provided is a good read!

  • nmi1010

    How does reverse osmosis treated water compare?

  • Dawn

    I am pregnant and live in MD, one of the states you listed as having a high chlorine water content. Does boiling the water help to eliminate any chlorine? I’m concerned about the BPA in plastic water bottles. I’ve also heard that bottled water is basically tap water. What do you recommend? Thanks!

  • kkre8ive1@gmail

    We have reverse osmosis water and lately I’ve been reading how RO water is not healthy. All minerals are stripped from the water and can actually harm you by not really hydrating your body and taking the minerals from your bones. Is there any truth to this and if so do I need to replenish my water and what should I use? Thank you

  • Richard

    What about filterd water like MultiPure?

    • Susan

      The correct spelling is Multipure.

  • Hello! Ok, tap water is better, and you can alcalinise it for a cheap prize, but it depends on where you live (I live in Madrid and the tap water is full of chlorine): what are the studies about water purifiers (like for example eSpring)??? That’s something what really interests me because we drink a lot of water and it’s sonfundamental in our diet…
    Thanks in advance,
    Léa Klein