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...Customers often ask questions about water issues
because they’ve heard a story on the TV or radio, or, perhaps, heard
some bit of information from a friend. Often, what they’ve heard
is incomplete information—or even wrong altogether.
.....Water that has been produced by a properly functioning reverse osmosis
system is some of the purest water available, yet often RO users are surprised
and a little alarmed to find that their very clean water is also “acidic”,
that is, that it has a low pH. Neutral pH is defined as 7.00, but RO water
typically shows a pH of between 5.00 and 6.00.
.....Given that the pH scale, like the Richter scale for earthquakes,
is logarithmic, that means that pH 5.00 water is actually 100 times as
acidic as pH 7.00 water. Certainly, that sounds very drastic, but due
to the somewhat unique properties of RO water, there really is no cause
.....First, it may be helpful to look at what pH measures. pH is a measurement
of the relative acidity or alkalinity of a solution. Some substances,
such as hydrogen ions, lower the pH of a solution. They are considered
acids. Other substances, such as hydroxide ions, raise the pH of a solution.
Those are called bases.
.....There are many different acids and bases that affect pH, but for
clarity sake it will be easiest to think only in terms of hydrogen ions
(H+) and hydroxide ions (OH-). When water has more free hydrogen ions
floating around than hydroxide ions, it is acidic (pH less than 7). When
there are more hydroxide ions than hydrogen ions, it is basic (pH greater
.....Water, as we have all learned, is described by the chemical formula
H2O. If you could shrink down small enough to be able to see molecules,
when you looked at a glass of water, you would see that the water molecules
did not simply stay put as H2O, but were always separating and recombining.
An H2O would break in to two pieces: an H+ and an OH-, and then get back
together. In that glass of water there would be gazillions of water molecules,
all splitting and rejoining constantly. If that water were very pure RO
water and didn’t have any other substances dissolved in it, the
pH would be neutral.
.....Because there are only H2O molecules there, the number of H’s
and OH’s would be even. There wouldn’t be more H’s than
OH’s, or the other way around, and so the acidity of an H+ would
be “cancelled out” by the alkalinity of an OH-. This balance
between hydrogen ions and hydroxide ions is what makes a solution neutral.
Therefore, extremely pure water is always neutral because it doesn’t
contain any other substances to throw off that H/OH balance.
.....Why then does RO water test to have a low pH? The very purity that
means it is neutral also makes it very sensitive to the addition of other
substances. Technically speaking, RO water has little or no buffering
capacity. That means that the addition of even a small amount of acid
will have a large effect on pH.
.....Consider this example. A man is blindfolded and put in a room. He
is told that he must raise his hand when he hears a baby start to cry.
If the room is quiet, free of other’“contaminating”
noises, and a baby starts to cry, he will raise his hand immediately.
If, however, the room contains a large flock of seagulls, several construction
workers with jackhammers, a roaring jet engine, an 80’s heavy metal
band, and other noisy things, and then a baby starts to cry, he will not
be able to notice it.
.....The empty, quiet room is like the glass of RO water. If only a tiny
amount of acid (a single baby crying) is added, the change will be easily
noticed. The noisy room is like a glass of tap water, full of amounts
of salt and minerals and other things commonly found in water. The addition
of one more thing will go basically unnoticed.
.....Regular, untreated tap water typically contains chemicals that act
as “buffers”. When some H+ is added to typical tap water,
some of those buffers “catch” the H+ and combine with it.
Then, even though H+ has been added, the pH doesn’t change because
the amount of free H+ floating around is still the same relative to the
amount of free OH-. Because a reverse osmosis removes the vast majority
of those buffer chemicals, when a little bit of H+ is added, it upsets
the balance between free H+ and free OH-.
.....Reverse osmosis membranes do not remove gasses, such as carbon dioxide
in water. Also, when RO water is exposed to the air, a small amount of
carbon dioxide will begin to dissolve in the water. So RO product water
has the buffering alkalinity chemicals removed and the acid causing gasses
.....Again, if you were small enough to see molecules, what you would
see happening is this: You would see the carbon dioxide molecules combine
with some of the OH-‘s in the water. That means that there would
be relatively more free H+’s floating around, because some OH-‘s
had been “caught” by the carbon dioxide in the water. Having
more free H+’s than OH-‘s floating about is how we earlier
defined an acidic solution, so that is why the pH of RO water is typically
lower than neutral.
.....Having low pH RO water should not be of concern because the “acidity”
in RO water is very weak. In order to bring RO water to a neutral pH,
it takes only a tiny amount of base. For example, if you had a glass of
RO water with a pH of 5.0 and you added 2-3 specks of baking soda (a base)
that would likely neutralize the tiny amount of acidity in the water.
.....For someone who is concerned about the effect of low pH RO water
on the body, I would not recommend going through the trouble to add specks
of baking soda to every glass of drinking water. The moment a person drinks
some low pH RO water, that water will combine with the saliva, and, moments
later, the stomach contents. It will cease to be extremely pure (because
it will have saliva and chewed up food in it), and so it will no longer
have the unique pH characteristics described above. Additionally, the
pH in the stomach of a healthy person is typically less than 2. That is
very, very acidic. As soon as the water gets to the stomach, it will become
very acidic, also.
.....That acidity is essential to human health. Without the acid in our
stomach, we would not be able to digest our food, and we would get sick
much, much more often because stomach acid kills many bacteria and other
things that we ingest. The only way that drinking low pH RO water could
upset the pH balance of the body might be if someone drank ridiculously
large amounts, and didn’t eat anything, and continued that for some
time. Barring that situation, drinking low pH RO water will have basically
no effect on the pH of the body.