Softened water sodium calculator: milligrams per glass and per day from your hardness number
Sodium added = 8 mg/L per gpg of hardness removed (NDSU). 15 gpg softened water carries 120 mg/L: 28 mg per 8 oz glass, 240 mg in 2 L a day.
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Short answer
A salt-regenerated water softener adds about 8 mg/L of sodium for every grain per gallon (gpg) of hardness it removes, the figure NDSU Extension publishes in fact sheet WQ1031. Sodium added = 8 x gpg removed; if the lab report gives hardness in mg/L as CaCO3, divide by 17 first (NDSU’s 1 gpg = 17 mg/L). Worked example: 15 gpg well water fully softened picks up 8 x 15 = 120 mg/L of sodium. An 8 oz glass (0.237 L) carries 120 x 0.237 = 28 mg, and 2 liters a day carries 240 mg. For scale, EPA’s 2003 drinking water advisory on sodium (822-R-03-006) states a guidance level of 20 mg/L for people on a 500 mg/day sodium-restricted diet and recommends 30 to 60 mg/L on taste grounds, so the 120 mg/L example is six times the guidance level. Potassium chloride regenerant adds no sodium but, per NDSU, uses about 10% more product per regeneration.
If nobody in the house counts sodium and the water tastes fine, you can stop here: the number below is arithmetic, not a diagnosis.
Sodium added by the softener, per liter, per glass and per day
Sodium mg/L = 8 x hardness removed in gpg (NDSU Extension WQ1031). Hardness entered in mg/L is divided by 17 (NDSU: 1 gpg = 17 mg/L). Per glass = mg/L x fl oz x 0.0296 L. Per day = mg/L x liters. Reference levels are EPA 822-R-03-006: 20 mg/L guidance level, 30 to 60 mg/L taste recommendation. Sodium already in the raw water is not included.
What is the formula?
Hardness removed is the calcium and magnesium the resin exchanges, in grains per gallon (gpg). The sodium added is the sodium the resin releases in their place, in milligrams per liter (mg/L).
| Step | Formula | Constant and its source |
|---|---|---|
| Concentration | sodium mg/L = 8 x gpg removed | 8 mg/L per gpg, NDSU Extension WQ1031 |
| Unit conversion | gpg = mg/L as CaCO3 / 17 | 1 gpg = 17 mg/L, NDSU Extension WQ1031 |
| Per glass | mg = sodium mg/L x fl oz x 0.0296 | 1 US fl oz = 0.0296 L, a unit definition |
| Per day | mg = sodium mg/L x liters drunk | none |
The 8 mg/L figure is NDSU’s rounded value, and the calculator uses NDSU’s 17 mg/L per gpg rather than the 17.118 on the water hardness unit converter so that one document carries every constant. Use the converter first if your report is in dH, fH, Clark or mmol/L.
The output is what the softener adds. It does not include sodium already in the raw water, which only a lab panel reports: the well water test panel lists what to order.
What does a worked example look like?
Take 15 gpg water, an 8 oz glass and 2 L of softened tap water a day.
- Concentration: 8 x 15 = 120 mg/L of added sodium.
- Per glass: 120 x 8 x 0.0296 = 28 mg.
- Per day: 120 x 2 = 240 mg.
- Against the references: 120 / 20 = 6.0 times EPA’s guidance level, and above the 30 to 60 mg/L taste band.
Two more inputs, run the same way:
| Input | Sodium added | Per 8 oz glass | Per day |
|---|---|---|---|
| 10 gpg removed, 2 L a day | 80 mg/L | 19 mg | 160 mg |
| 15 gpg removed, 2 L a day | 120 mg/L | 28 mg | 240 mg |
| 205 mg/L as CaCO3 removed (12.1 gpg), 3 L a day | 96.5 mg/L | 23 mg | 289 mg |
The 10 gpg row shows why per-liter and per-day both matter: 80 mg/L is four times the 20 mg/L guidance level, and 2 L of it is 160 mg, about a third of the 500 mg/day budget that level was written for.
What do the reference levels mean?
Sodium has no enforceable federal drinking water limit. EPA’s 2003 advisory, 822-R-03-006, publishes three figures the calculator compares against:
| Level | Value | Basis stated by EPA |
|---|---|---|
| Guidance level | 20 mg/L | Developed for people restricted to 500 mg/day of total sodium |
| Taste recommendation | 30 to 60 mg/L | Esthetic effects; the advisory cites individual thresholds from about 30 to 460 mg/L |
| WHO guideline (cited by EPA) | 200 mg/L | Esthetic considerations, taste |
Whether any of these matters in your house is a question for whoever manages the diet, not for this page. The page only turns a hardness number into milligrams.
Does potassium chloride avoid the sodium?
Potassium chloride (KCl) regenerant exchanges hardness for potassium instead of sodium, so the sodium added drops to 0 mg/L. NDSU WQ1031 records the trade: it is more expensive, adheres more strongly to the resin, which reduces exchange efficiency, and about 10% more of it is used during regeneration.
| Regenerant | Sodium added per gpg removed | Product used per regeneration | Source |
|---|---|---|---|
| Sodium chloride (softener salt) | 8 mg/L | baseline | NDSU WQ1031 |
| Potassium chloride | 0 mg/L | about 10% more | NDSU WQ1031 |
The water softener salt usage calculator gives the pounds per year to scale that 10% against. The salt-free conditioner vs softener guide is for the reader who wants no ion exchange at all.
Only after you have a hardness number
Do not switch regenerant on a guess. A hardness figure from a lab report or a test strip, run through the calculator above, is what decides whether a change buys anything: at 3 gpg the softener adds 24 mg/L, at 20 gpg it adds 160 mg/L.
If the number says switch, Morton Potassium Chloride pellets, 40 lb is the potassium chloride compared in the water softener salt review. Admit the flaw first: it costs more per bag, uses about 10% more per regeneration, and the review notes its higher bridging tendency. Skip it if an unsoftened kitchen tap already solves the drinking-water question.
Where do the numbers come from?
- 8 mg/L of sodium per gpg removed, 1 gpg = 17 mg/L, the unsoftened kitchen tap and the potassium chloride notes: NDSU Extension WQ1031, Water Softening (Ion Exchange), revised May 2022.
- 20 mg/L guidance level, the 500 mg/day diet it was developed for, the 30 to 60 mg/L taste recommendation, the 30 to 460 mg/L threshold range and the WHO 200 mg/L figure: EPA 822-R-03-006, Drinking Water Advisory on Sodium, February 2003.
- 1 US fluid ounce = 0.0296 L: a unit definition, not a researched figure.
Frequently asked questions
How much sodium does a water softener add per grain of hardness?
NDSU Extension's WQ1031 fact sheet puts it at about 8 mg/L (ppm) of sodium for every grain per gallon of hardness the resin removes. Water softened from 10 gpg therefore carries about 80 mg/L of added sodium, and water softened from 20 gpg about 160 mg/L. The sodium comes from the salt brine used to regenerate the resin.
What is EPA's guidance level for sodium in drinking water?
EPA's 2003 Drinking Water Advisory on sodium (822-R-03-006) states a guidance level of 20 mg/L, developed for people restricted to a total sodium intake of 500 mg per day. Sodium has no enforceable federal limit. The same advisory recommends 30 to 60 mg/L on taste grounds, and cites individual taste thresholds from about 30 to 460 mg/L.
Does potassium chloride avoid the sodium problem?
Yes for sodium: potassium chloride regenerant exchanges hardness for potassium instead. NDSU WQ1031 adds two costs. Potassium chloride is more expensive and adheres more strongly to the resin, which lowers exchange efficiency, and about 10% more of it is used during regeneration than sodium chloride. The water softener salt review compares the pellets.
Do I have to drink softened water at all?
No. NDSU WQ1031 describes leaving one unsoftened cold tap in the kitchen for drinking and cooking. That is a plumbing change rather than a regenerant change, and it keeps the sodium added by the softener at 0 mg/L at that one tap while every other fixture in the house still receives softened water for scale control.
At what sodium level does water start to taste salty?
There is no single number. EPA's 2003 advisory says the average taste threshold at room temperature differs substantially between people and ranges from about 30 mg/L to 460 mg/L, which is why it recommends 30 to 60 mg/L. The World Health Organization's taste-based guideline, cited in the same advisory, is 200 mg/L.
Fact sheet and how to cite this page
- Answer
- A salt-regenerated softener adds about 8 mg/L of sodium per grain per gallon of hardness removed, per NDSU Extension WQ1031. Water softened from 15 gpg carries 120 mg/L: about 28 mg in an 8 oz glass and 240 mg in 2 L a day, against EPA’s 20 mg/L guidance level for a 500 mg/day sodium-restricted diet.
- Formula
sodium mg/L = 8 x hardness removed (gpg); mg per glass = sodium mg/L x oz x 0.0296; mg per day = sodium mg/L x liters per day- Inputs
- Hardness removed: 15 gpg
- Glass size: 8 oz
- Daily drinking water: 2 L
- Output
- 120 mg/L sodium; 28 mg per 8 oz glass; 240 mg per day
- Assumptions
- The softener removes all of the hardness entered; a bypass or blending valve lowers the figure in proportion
- Hardness entered in mg/L as CaCO3 is converted at NDSU’s 1 gpg = 17 mg/L
- 1 US fluid ounce = 0.0296 L, a unit definition
- Sodium already present in the raw water is not included; the calculator returns only what the softener adds
- Method
- The calculator multiplies the hardness removed in grains per gallon by NDSU Extension’s published 8 mg/L of sodium per grain, converts that concentration to milligrams for one glass and for one day’s intake, and compares the concentration with the 20 mg/L guidance level and the 30 to 60 mg/L taste recommendation in EPA’s 2003 sodium advisory.
- Primary source
- NDSU Extension, WQ1031 Water Softening (Ion Exchange), revised May 2022 (PDF) (university or extension service)
- Facts verified
- Last updated
- Cite as
- OwnerSpec, "Softened water sodium calculator: milligrams per glass and per day from your hardness number", https://ownerspec.com/water/calculators/softened-water-sodium-calculator/, facts verified 15 September 2026.
Every figure above also appears, with its source, in the article. All sources ยท How OwnerSpec verifies numbers
Sources
- NDSU Extension, WQ1031 Water Softening (Ion Exchange), revised May 2022 (PDF) (university or extension service)
- US EPA, Drinking Water Advisory: Consumer Acceptability Advice and Health Effects Analysis on Sodium, EPA 822-R-03-006, February 2003 (PDF) (government or regulatory source)