Hardness

At a glance: Hardness is dissolved calcium and magnesium. It is not a health risk, and EPA sets no limit, but above about 120 mg/L (7 grains per gallon) most homes notice scale on fixtures, spots on glass and poor lather. A salt-based softener is the only household method that removes hardness. A salt-free conditioner can reduce scale in pipes and water heaters without salt, but it does not make water soft.

If your water is under 60 mg/L, USGS classes it as soft and you do not need either.

What it is and where it comes from

Water picks up calcium and magnesium as it moves through soil and rock. Hardness is reported as mg/L of calcium carbonate, or in grains per gallon (gpg). One grain per gallon equals 17.1 mg/L.

Both well water and city water can be hard. Hardness is not regulated, so city water hardness depends on the source and on whether your utility softens it. Your utility can tell you its typical hardness, and it is often listed in the annual water quality report.

Health and household effects

Penn State Extension is direct about health: calcium and magnesium “have no adverse effects and are, in fact, essential daily nutrients.” WHO does not propose a health-based guideline value for hardness.

The effects are practical. Penn State describes hardness minerals building up on surfaces, possibly plugging pipes and damaging water heaters, and reducing how well soaps and detergents work. In practice that means:

• White scale on faucets, showerheads, kettles and inside water heaters
• Spots and film on dishes and glassware
• More soap and detergent needed for the same lather
• Soap scum on tubs and tile

Softening has one health trade-off. Penn State says swapping hardness for sodium adds 7.5 milligrams of sodium per quart for each grain per gallon removed. At 10 gpg that is 75 mg per quart. Wisconsin’s health department notes this may matter for people on low-sodium diets.

Limits and what they mean

There is no enforceable or secondary federal standard for hardness. These are the classifications used instead:

Classification (USGS)	mg/L as calcium carbonate	Grains per gallon
Soft	0 to 60	0 to 3.5
Moderately hard	61 to 120	3.6 to 7.0
Hard	121 to 180	7.1 to 10.5
Very hard	Over 180	Over 10.5

The Water Quality Association defines soft water as under 1 grain per gallon, the target for a properly working salt softener.

How to test

Hardness is one of the few things a test strip measures well enough to act on. For sizing a softener, get a lab number: Wisconsin’s state lab charges $46 for calcium, magnesium and hardness, and Penn State’s $85 package adds iron and manganese, which also affect softener choice. On city water, ask the utility first.

Sizing a softener needs grains per gallon, household water use and your iron level, because softeners also have to handle any dissolved iron. Our well testing guide covers labs and sampling.

Treatment options

Method	How well it works	Certification to look for	Cost range
Salt-based water softener	High; removes hardness to under 1 gpg	NSF/ANSI 44	$200 to $3,000, plus $50 to $300 a year for salt
Salt-free conditioner (TAC)	Moderate; reduces scale, does not remove hardness	IAPMO/ANSI Z601 or DVGW W 512	$879 to $1,785 (systems we track)
Reverse osmosis, point of use	High at one tap	NSF/ANSI 58	$300 to $1,500
Magnetic or electronic descalers	Low; about 50% scale reduction in the WateReuse study	None	Not recommended

Cost ranges are Minnesota Department of Health estimates based on 2017 and 2018 quotes, low end self-installed and high end professionally installed. Figures for systems we track are prices checked September 2026.

Softener. An NSF/ANSI 44 certified softener cannot drop line pressure by more than 15 psi at its rated flow, and an efficiency rating requires at least 3,350 grains removed per pound of salt. Only demand-initiated softeners can earn that rating. A softener needs a drain and power and uses water for each regeneration.

Salt-free conditioner. Template-assisted crystallization (TAC) turns some hardness into tiny crystals that stay in the water, so less scale sticks to heating surfaces. The WateReuse Research Foundation’s study measured over 88% scale reduction in its test rig. The Water Quality Association notes these devices do not reduce calcium or magnesium and are not proven to achieve soft water. Makers typically require iron and manganese to be low, and on chlorinated water some need a carbon filter first.

You may not need either. On moderately hard city water, scale protection for a water heater may be all you want, and salt-free is a reasonable choice. If spotting and soap scum bother you, only salt fixes that. Our salt-free vs salt softener guide compares them in detail, and our salt-free softener picks and the filter finder show the options we track.

When to call a professional

A salt softener needs a drain line, an outlet and a bypass valve, so most installs call for a licensed plumber. Water treatment professionals can size a softener from your test, but ask for the sizing arithmetic in writing.

On a well, call a water treatment professional if your hardness comes with iron above a few mg/L or with low pH, because the order of equipment matters: sediment and iron treatment first, then the softener.