František Kožíšek,
M.D., Ph.D.
National Institute of Public Health
February 2003
Introduction
Drinking water quality is currently defined only as the absence
or a strictly limited presence
of certain undesirable substances, however, distilled or demineralized
water can hardly be
considered as an ideal of good drinking water. Drinking water is
a complex system of mineral
substances and gases dissolved in water. Calcium (Ca) and magnesium
(Mg) are among the
important and most thoroughly studied natural water constituents.
The present contribution summarizes the existing knowledge of health
significance of
drinking water Ca and Mg and the attempts to reflect it in regulation
and suggests how to
bridge the regulatory gaps in this field.
Calcium, magnesium and water hardness
If we want to work on calcium and magnesium in drinking water, a
third parameter is to be
taken into account: water hardness, even if this term is incorrect
and obsolete from a strictly
chemical point of view. That is to say that both of these elements
largely have not been
analysed individually in drinking water in the past, but just non-specifically
in summary as
hardness. This approach was applied in many studies focused on health
effects of this “water
factor”.
Since the definition of water hardness is approached either analytically
or technologically, it
was not and still has not been defined in a unified manner, and as
with other parameters,
multiple definitions have been available and multiple units have
been used to express it
(German, French, and English degrees; equivalent CaCO3 or CaO in
mg/l).
Initially, water hardness was understood to be a measure of the capacity
of water to
precipitate soap, which is in practice the sum of concentrations
of all polyvalent cations
present in water (Ca, Mg, Sr, Ba, Fe, Al, Mn, etc.); nevertheless,
since the other ions (apart
from Ca and Mg) play a minor role in this regard, later it has been
generally accepted that
hardness is defined as the sum of the Ca and Mg concentrations, determined
by the EDTA
titrimetric method, and expressed in mmol/l (ISO, 1984) or as CaCO3
equivalent in mg/l
(Standard Methods, 1998), less frequently as the CaO equivalent.
From the technical point of view, multiple different scales of water
hardness were suggested
(e.g. very soft – soft – medium hard – hard – very
hard). Expectedly, both extreme degrees
(i.e. very soft and very hard) are considered as undesirable concordantly
from the technical
and health points of view, but the optimum Ca and Mg water levels
are not easy to determine
since the health requirements may not coincide with the technical
ones.
Calcium and magnesium presence in waters
Water calcium and magnesium result from decomposition of calcium
and magnesium
aluminosilicates and, at higher concentrations, from dissolution
of limestone, magnesium
limestone, magnesite, gypsum and other minerals. Anthropogenenic
contamination of
drinking water sources with calcium and magnesium is not common but
drinking water may
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