Do the arithmetic rather than take a side

Two claims circulate about softened water, and both skip the number.

Penn State Extension supplies it: “The exchange of hardness minerals for sodium adds 7.5 milligrams per quart for each gpg of hardness removed.”

That is a rate, not a concentration. It becomes a figure only when you multiply by your own hardness, which is why nobody can tell you whether softened water is a sodium problem without asking what your water measures.

Convert it to the unit dietary guidance uses, with NIST’s factor:

1 US liquid quart = 0.946353 L            (NIST SP 811)

7.5 mg per quart  = 7.93 mg per litre     per grain per gallon removed

What that means at your hardness

Your hardness Sodium added per litre 2 litres a day Share of FDA Daily Value
7 gpg 55 mg 111 mg 4.8%
10 gpg 79 mg 159 mg 6.9%
15 gpg 119 mg 238 mg 10.3%
20 gpg 159 mg 317 mg 13.8%
25 gpg 198 mg 396 mg 17.2%

FDA sets the Daily Value for sodium at “less than 2,300 milligrams (mg) per day”, and gives a scale for reading a contribution: “5% DV or less of sodium per serving is considered low, and 20% DV or more of sodium per serving is considered high.”

So on FDA’s own scale, softened drinking water at typical household hardness lands between low and high — closer to low at 7 gpg, approaching high at 25 gpg.

That is the honest answer. Not nothing, not alarming, and entirely dependent on a number you can measure.

The part nobody mentions at the point of sale

Penn State adds a second consequence in the same sentence: “In addition, calcium and magnesium are eliminated from the homeowner’s diet.”

Those are the two minerals that define hardness, so removing them is the mechanism working exactly as designed. Whether that matters to you is a dietary question, not a water treatment one — but it belongs in the decision, and softener listings do not carry it.

Both fixes are free

Change the regenerant. Minnesota Department of Health suggests “regenerate your softener with potassium chloride instead of sodium chloride (salt)” for sodium-restricted households. The exchange still happens; potassium goes in instead of sodium, and the table above stops applying.

Keep one tap unsoftened. Minnesota Health recommends keeping an un-softened tap for cooking and drinking regardless of anyone’s diet. Penn State notes the plumbing makes this straightforward: softening systems make it “easy to bypass toilets and outdoor faucets,” and can be adapted to blend softened and unsoftened water to a lower hardness.

If the drinking tap is bypassed, the sodium question resolves itself and the appliance protection you bought the softener for is untouched.

The decision path

Your situation What decides it What to do
Nobody sodium-restricted, hardness under 15 gpg Around 10% of Daily Value or less Nothing required; bypass the drinking tap if convenient
Nobody restricted, hardness above 20 gpg Approaching FDA’s “high” band Bypass the drinking tap, or blend down
Someone on a sodium-restricted diet Any contribution is worth removing Potassium chloride, or an un-softened drinking tap
Concerned about losing calcium and magnesium Softening removes both by design Un-softened drinking tap keeps them
On a septic system About 50 gallons per regeneration Check drainage field capacity before installing
Unsure of your hardness The whole calculation depends on it Test before deciding anything

Choose potassium chloride if

  • Someone in the household is on a sodium-restricted diet.
  • You want every tap softened without the sodium contribution.
  • You accept it typically costs more per bag than sodium chloride.

Choose an un-softened drinking tap if

  • You want the sodium question to disappear at no running cost.
  • You also want dietary calcium and magnesium retained.
  • Minnesota Health’s recommendation applies to you, which is to say anyone.

Choose to do nothing if

  • Your hardness is modest, nobody is sodium-restricted, and the contribution sits near FDA’s low band.
  • You already drink mostly from a filtered or bypassed tap.

Mistakes that cost the most money

Arguing the question without the number. The answer scales directly with your hardness, so it cannot be settled in general.

Buying a salt-free conditioner to avoid sodium. It avoids sodium by not softening — your hardness number does not fall.

→ What salt-free conditioners actually do

Softening every tap by default. Minnesota Health recommends an un-softened tap for cooking and drinking regardless, and the plumbing makes it easy.

Treating hard water as a health hazard to justify the purchase. It is a comfort, scale and appliance-life decision.

Ignoring the septic load. Penn State puts regeneration at about 50 gallons a cycle and says it may or may not overload a drainage field.

Assuming potassium chloride changes nothing else. It is a direct substitution for the exchange, but it usually costs more per bag, which belongs in the running-cost calculation alongside salt efficiency.

Three situations, and what changes

A sodium-restricted household on hard water. Potassium chloride plus an un-softened drinking tap removes the question twice over. The appliance protection is unaffected either way.

A household with no dietary restriction on 12 gpg water. The contribution is about 8 percent of the Daily Value at two litres a day. Bypassing the kitchen tap is still worth doing, because it costs nothing and keeps the calcium and magnesium.

A well household on a septic system. The sodium is the smaller question. The 50 gallons per regeneration reaching the drainage field is the one to check before buying, and it argues for a correctly sized, efficient unit.

The objections worth answering

“Softened water is basically salt water.” At 15 gpg it is about 119 mg of sodium per litre, roughly a tenth of FDA’s Daily Value in two litres. It is a real contribution and it is a long way from salt water.

“My doctor said avoid softened water entirely.” Then follow that, and note the two no-cost routes that satisfy it: potassium chloride regeneration, or drinking from an un-softened tap. Neither requires giving up the softener.

“If it removes calcium and magnesium, is soft water unhealthy?” Penn State records the removal as a disadvantage worth weighing, not a hazard. Most dietary calcium and magnesium comes from food, and an un-softened drinking tap retains the water contribution if you want it.

Who this is for

Households that already have a softener or are about to buy one, and want the sodium question answered with their own hardness number rather than in the abstract — particularly anyone with a dietary restriction in the house.

What to work out before deciding

What is my hardness in grains per gallon, and is anyone in this house on a sodium-restricted diet?

Those two answers produce the whole decision. Everything above is arithmetic on top of them.

→ Sizing a softener, and what it costs to run → Salt-free conditioners, and why the hardness number does not move → City water treatment, and where softening sits in it