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Last change 10/2018 E-P | Subject to technical modifications
Appendices 3:
Calculation sodium contents:
The sodium concentration in mixed water is increased due to softening dependent on the incoming
water hardness and the set mixed water hardness.
According to drinking water regulation 2001, the limit value for sodium is 200 mg/L.
If the mixed water or the sodium contents is still in accordance with the regulation can be calculated
as below:
ppm (CaCO
3
)
Incoming water hardness (to be obtained from the water
work or to be measured by means of a test kit)
-
ppm (CaCO
3
)
Mixed water hardness (measured value)
=
ppm x 0,46
(Na-Ion (sodium ion) exchange value)
=
ppm (Na
+
)
Increase of sodium contents by softening
+
ppm (Na
+
)
Sodium contents in incoming water (to be obtained from
water work)
=
mg/L (Na
+
)
Total sodium contents in mixed water
Example:
300
ppm
-
60
ppm
-------------------------------
=
240
ppm x 0.46
=
110
ppm
fed by softening
+
10
ppm
(assumed)
in incoming water
--------------------------------
=
120
ppm
total sodium contents
==================
If the calculated total sodium contents exceed the limit value 200 ppm as per drinking water
regulation, the sodium feed has to be reduced by increasing the mixed water hardness.
A total hardness of 1 ppm (CaCO
3
) corresponds to 0.46 mg/l sodium contents. The calculation shall
be done anew with the corrected value.
