Section 11
Specifications
20413013
8-2012/Rev 10
11-6
Table 11-4
Water Impurities
Constituent
Chemical Formula
Comments
Alkalinity Bicarbonate (HCO
3
)
Carbonate (CO
3
)
Hydrate (OH),
expressed as CaCO
3
Acid neutralizing capacity of water. Foaming
and carryover of solids, causes embrittlement of
steel, can produce CO
2
, a source of corrosion.
Calcium Ca When dissolved makes water hard; contributes to
the formation of scale.
Chloride Cl Adds to solid content and increases corrosive
character of water; in relative percentage
presence with oxygen induces stress corrosion
cracking.
Free Chlorine Cl
2
Oxidizing agent; can attack elastomeric seals and
damage reverse osmosis (RO) membranes.
Iron Fe
++
(ferrous)
Fe
+++
(ferric)
Discolors water or precipitation; source of scale
and erosion.
Magnesium as Mg When dissolved makes water hard; contributes to
the formation of scale.
Manganese as Mn Mn
++
Discolors water or precipitation; source of scale
and erosion.
Nitrate NO
3
Adds to solid content; effect is not generally
significant industrially.
Silica SiO
2
Causes scale
Sodium Na Found naturally; introduced to water in the ion
exchange water softening process.
Sulfate SO
4
Adds to solid content; combines with calcium to
form calcium sulfate scale.
TDS Measure of the total amount of dissolved matter
in water.
Total Hardness CaCO
3
Sum of all hardness constituents in water;
typically expressed as their equivalent
concentration of calcium carbonate; primarily due
to calcium and magnesium in solution, but may
include small amounts of metal. Carbonate
hardness is usually due to magnesium and
calcium bicarbonate; non-carbonate hardness is
due to sulfates and chlorides.
pH Intensity of the acidic or alkaline solids in water;
pH scale runs from 0, highly acidic, to 14, highly
alkaline; with 7 being neutral.
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