Water Knowledge

Hardness

Summary: Water “hardness” is the amount of dissolved calcium and magnesium. Hard water leaves scale on fixtures and heaters, makes soap work poorly, and causes spots on glassware. Softening protects plumbing and appliances and can improve skin feel and cleaning—while point-of-use RO gives great taste for drinking and coffee.

Why homeowners should care

Scale from hard water builds up inside water heaters, dishwashers, showerheads, and pipes, wasting energy and shortening equipment life. You’ll also use more soap and detergents. The good news: hardness is straightforward to measure and control.

What hardness really means

  • What it is: Calcium (Ca) and magnesium (Mg) expressed as calcium carbonate (CaCO3).
  • Units: mg/L (ppm) or grains per gallon (gpg). 1 gpg ≈ 17.1 mg/L.
  • Typical categories (as CaCO3):
    • Soft: < 1 gpg (< 17 mg/L)
    • Slightly hard: 1–3.5 gpg (17–60 mg/L)
    • Moderately hard: 3.5–7 gpg (60–120 mg/L)
    • Hard: 7–10.5 gpg (120–180 mg/L)
    • Very hard: > 10.5 gpg (> 180 mg/L)
  • Chemistry context: Scale risk depends on hardness + alkalinity + pH + temperature. Hot water scales fastest.

When to test

  • At move-in or when you start a private-well baseline.
  • Annually (or when you notice soap film, spots, or heater noise/efficiency loss).
  • Before sizing a softener; after installation to confirm it’s working.

How we test

HealthWaterLab measures total hardness (and can add calcium hardness) by photometric/titration methods. For treatment design, we can pair hardness with alkalinity, pH, conductivity/TDS, iron, and manganese.

How to collect a good sample

  • Use the kitchen cold-water tap (or raw water prior to your softener if we’re sizing equipment).
  • Run water several minutes to bring in fresh water; remove aerators if instructed.
  • Fill to the mark without touching inside the bottle/cap; deliver promptly.

How to read your result (homeowner version)

  • < 3.5 gpg: Usually fine for most homes; scale is mild.
  • 3.5–7 gpg: Noticeable spots/film; softening improves cleaning and protects heaters.
  • > 7 gpg: Scale control strongly recommended—softener or alternative anti-scale strategy.

Practical ways to manage hardness

  • Ion-exchange softener (whole home): Replaces Ca/Mg with sodium or potassium, preventing scale. Size by compensated hardness (include iron/manganese equivalents) and household usage; adjust salt dose for efficiency.
  • Point-of-use RO (kitchen): For great-tasting drinking water and coffee; also protects kettles and espresso from scale.
  • Alternative anti-scale: Template-assisted crystallization (TAC) or polyphosphate dosing can reduce visible scale adhesion without softening, but don’t lower hardness/TDS.
  • Maintenance: Descale heaters as needed, use rinse-aid in dishwashers, clean aerators/showerheads, and monitor with a simple hardness strip after the softener.

FAQ

Is hard water bad for my health?

Hardness minerals are not a health hazard for most people; the main issues are scale and soap use. Treatment is about protection and comfort.

Will a softener lower TDS or salinity?

No. Softeners swap Ca/Mg for Na/K, so total dissolved solids change little. For lower TDS/salts at the tap, use reverse osmosis (RO).

How much sodium does softening add?

Roughly 7.5–8 mg of sodium per gpg of hardness per liter of water softened. For drinking, many homeowners use RO or choose potassium chloride (KCl) instead of sodium chloride—though KCl still leaves TDS similar.

Should I soften the whole house or only hot water?

Whole-home softening protects all fixtures and heaters. Some people soften only hot water to cut salt use while keeping “crisper” cold water at some taps.

My softener isn’t working—what should I check?

Salt level/bridging, brine injector, resin fouling (iron/manganese), stuck bypass, and correct programming (capacity, hardness setting). Test raw vs softened hardness to confirm.

Does iron or manganese affect softener sizing?

Yes. Convert iron/manganese to “hardness equivalents” for sizing/regeneration (common rule of thumb: add 1 gpg per 1 ppm iron; 1 gpg per 1 ppm manganese) or use upstream oxidation/filtration.

What’s “compensated hardness”?

The hardness value you program into a softener that includes hardness plus adjustments for iron/manganese. It ensures proper capacity and regeneration frequency.

Are anti-scale systems the same as softeners?

No. TAC/polyphosphate reduce scale adhesion but don’t remove Ca/Mg, so water still tests hard. They’re good where you want less spotting with minimal maintenance.

Will softened water feel “slippery”?

Often yes—soap lathers better without calcium, so rinsing feels slick. Most people adjust quickly; you can use a bit less soap/shampoo.

Does high hardness damage tankless heaters?

Scale can rapidly foul tankless heat exchangers. Manufacturers often specify a max hardness and require regular descaling—softening is strongly recommended in hard-water areas.

Espresso/coffee: should I use RO or softened water?

For machine longevity, low-scale water is key. Many use RO with a small remineralization cartridge to hit taste targets while protecting boilers/groupheads.

How often should I recheck hardness?

Annually for private wells and any time you change treatment. After a softener, use quick strips monthly and a lab check periodically to verify performance.

Want help sizing a softener or pairing it with RO? Get hardness testing and step-by-step guidance at HealthWaterLab.com.