Ask A Scientist Chemistry Archive

name         Paul
status       student
grade        9-12
location     N/A

Question -   Can water hardness be determined in ppm of calcium and
magnesium contaminant by measuring its pH?  What other tests can be
done to measure the hardness?
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Hi Paul,

Unfortunately, pH is not an accurate indication of water hardness.
Originally, water hardness was a measure of the capacity of water to
precipitate soap, mostly due to calcium and magnesium ions.  Currently,
total hardness is defined as the sum of the calcium and magnesium
concentrations, in milligrams per liter, expressed as calcium carbonate.

For a list of test methods for measuring hardness, calcium and
magnesium, please refer to Standard Methods for the Examination of Water
and Wastewater.

Bob Hartwell
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pH alone  is not a sensitive measure of water "hardness", which is the
cumulative concentration of metal ions, primarily Ca(+2) and Mg(+2). There
are a number commercial sources of pre-packaged units for determining
water hardness -- one source is Hach Inc.-- but not the only one. It is
usually easier and more reliable to use one of these pre-packaged test
kits that to start from scratch and develop your own. There are in
addition kits for determining Fe(+2/+3), Cu(+2) and most of the common
metals and non-metals as well.

Vince Calder
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