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Since sodium is added to water softened by the cation exchange process (mechanical water softening), the level of sodium is softened water may be of interest to persons on sodium restricted diets.
Sodium in Softened Water
Table #1 shows the amount of sodium added to softened water of varying original hardness. The harder the water originally, the more sodium that is added.
Table 1-Sodium Added to Water From Cation Exchange Softening
Initial Water Hardness
Sodium added by Cation Exchange Softening of Water
Grains per gallon
Milligrams Na +/Gallon
Milligrams Na +/Quart
1
30
7.5
5
149
37
6
179
44
7
209
52
8
239
60
9
269
68
10
298
75
15
447
112
20
596
150
30
894
225
40
1,191
300
Contribution of Sodium From Water Softening to Total Sodium Intake
Assuming a daily intake of 5 grams (5,000 milligrams) of sodium in food and the consumption of 3 quarts of water (used for coffee, tea, food preparation, and drinking) the contribution of the sodium (Na+) in the water from the home water softening process compared to the total daily intake can bee seen in table #2.
Sodium restricted diets
Persons who must restrict their sodium intake to 500 milligrams per day should consume water that contains no more than 20 milligrams of sodium per quart. This is assuming that most people consume about three quarts of water per day from all sources (beverages, food preparation, and drinking). Twenty milligrams per quarts X Three quarts equals Sixty milligrams total daily from water.
The 60 milligram level has been suggested since the basic 500 milligram therapeutic diet actually contains about 440 milligrams of sodium from food. This allows 60 milligrams of sodium from water.
The sodium (Na+) is restricted to 1000 milligrams per day, the upper limit for total sodium content of water is about 200 milligrams or about 66 milligrams per quart if three quarts are consumed.
See Table #3 for original hardness limits of softened water for different levels of water consumption.
If an ion exchange water softener is to be used in a home where a person is on sodium-restricted therapy and water hardness is great enough that excess sodium may be consumed by suing softened water, a bypass can be installed to provide unsoftened water for drinking and cooking.
In some localities the sodium content of the municipal water supply and water from wells may also be higher in sodium than can be allowed.
Persons on sodium-restricted therapy can obtain advice from a physician or dietitian. The municipal water department will provide a detailed analysis of the water supply. Detailed analysis of well-water can also be obtained. Contact the municipal water department, The Public Health Service, a local water softening dealer, or the Cooperative Extension Service for the name and address of a laboratory which makes this analysis.
Table 2-Sodium Intake from Softened Water Compared to Total Sodium Intake
Initial Water Hardness/Grains per Gallon
Milligram Na+ Per 3 qts. Softened Water
Milligrams Na+ from Food
Total Na+ Consumed Milligrams
% of Total from Softened Water
1
23
5,000
5,023
0.4%
5
112
5,000
5,112
2.2%
10
223
5,000
5,223
4.3%
15
335
5,000
5,335
6.5%
20
447
5,000
5,447
8.2%
30
670
5,000
5,670
12.5%
40
893
5,000
5,893
15.2%
Table 3-Original Hardness Limits of Softened Water Allowable for Sodium Restricted Therapy
Total Sodium Level Permitted
Total Sodium Allowed from water
Original Hardness Limits in Grains per Gallon (gpg) if Consumption of Softened Water is:
 
3 Qts.
2 Qts.
1 Qt.
500 mg.
60 mg.
2.6 gpg
4 gpg
8 gpg
1000 mg.
200 mg.
8.8 gpg
13 gpg
26 gpg
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