Quick answer
Hard water is water with enough dissolved calcium and magnesium to create noticeable effects in the home. It is usually measured as mg/L or ppm of calcium carbonate. USGS classifies water above 180 mg/L as very hard.
Common signs of hard water
- White buildup on faucets and showerheads
- Spots or film on dishes and glassware
- Soap that does not lather easily
- Scale inside kettles, coffee makers, or water heaters
- Shower glass that is hard to keep clean
How hard water is measured
Water reports may show hardness as mg/L or ppm as calcium carbonate. Water softener sizing often uses grains per gallon. You can convert ppm to grains per gallon by dividing by about 17.1.
Should you test for hardness?
If your utility report lists hardness, that is a good starting point. Testing may be useful if your home has treatment equipment, your water source varies, you use a private well, or you want an address-specific number before sizing a softener.
Does hard water mean you need a softener?
Not always. Some homeowners tolerate hard water. Others install a softener because scale, spots, and appliance maintenance become frustrating. The decision depends on hardness level, home ownership, plumbing setup, water use, budget, and personal preference.
Sources and limitations
- USGS water hardness classification guidance.
- This page explains general water hardness. It is not a test of water at a specific faucet.