Re: pH of tap water

Allen Sandifer wrote (Digest VI #87):

>I am trying to lower the pH of my tap water naturally. As it comes from the
>tap the pH is 9.3, if I let it sit for about a month aerating it several
>hours a day it will drop to 8.1, which is rather confusing to me. Can anyone
>explain this to me?
It sounds as though your municipal water supplier adds lime to the water to
prevent it from dissolving metal from the pipes.  That is good.  I used to
live in Boston, MA, where the rocks are granite and reservoir water does
not come in contact with limestome.  The pH was about 6; no lime was added
and the tap water had 5 PPM copper.  This amount of copper will kill snails
in an hour and fish in one or two days.  Perhaps Boston is adding some lime
now; I only know that they weren't doing it when I was there in the early
'70's.  I used to collect water for my aquariums from runoff from a
fenced-in reservoir near Boston. I wondered whether it was healthy to drink
water with that much copper.

The drop in pH upon standing is likely due to the water absorbing CO2 from
the atmosphere.  Your water actually sounds less alkaline than mine, here
at Tougaloo College.  It comes out of the tap with a pH of 8.4, but the pH
actually rises to 8.6 upon standing.

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>If I mix water with a pH of 8.0 with water that has a pH of 7.0 will I get
>water with a pH of 7.5?

Not necessarily.  This would happen only if the buffering capacities of
both kinds of water were the same.  The buffering capacity is a measure of
how much acid or base can be added to a solution before the pH changes by
more than one pH unit.  If your pH 8.0 solution had a certain amount of
buffering cpacity due to the presence of calcium bicarbonate, adding an
equal amount of pH 7.0 distilled water might not change the pH very much at

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174