HARD WATER GUIDE
How hard is “hard water”?
Hard water contains dissolved calcium and magnesium, usually reported as milligrams per liter of calcium carbonate or grains per gallon. USGS classifies 0–60 mg/L as soft, 61–120 mg/L as moderately hard, 121–180 mg/L as hard and more than 180 mg/L as very hard. Source: USGS Hardness of Water.
| Hardness as CaCO3 | USGS description | What homeowners may notice |
|---|
| 0–60 mg/L | Soft | Little hardness scale |
| 61–120 mg/L | Moderately hard | Some spotting or mineral buildup may appear |
| 121–180 mg/L | Hard | Scale and soap-performance complaints become more common |
| Over 180 mg/L | Very hard | More pronounced scale and mineral buildup are common |
What problems can hard water cause?
Scale
Mineral deposits can accumulate on fixtures, shower glass and water-heating surfaces. Hardness is an aesthetic/operational water condition rather than a reason to assume the water is unsafe.
Soap performance
Hardness minerals react with soap, which can increase soap use and leave residue on fixtures or laundry.
What is the right treatment for hard water?
Ion-exchange softening is the standard treatment category for reducing hardness minerals. Treatment capacity and regeneration settings should be based on measured hardness, water demand and any iron or manganese that may load the resin. A carbon filter is not a substitute for a softener because it targets different water-quality concerns.
Learn more on the Water Softeners page or compare categories in Water Softener vs. Whole-House Filter.
Testing matters: white residue does not always prove hardness. A hardness result tells you whether softening is appropriate and how the system should be sized.
Hard water FAQs
What are the most common signs of hard water?
Is hard water unsafe to drink?
Hardness is generally treated as an aesthetic and operational water-quality issue, not a direct indication that water is unsafe. Separate health concerns require their own testing.
Will a whole-home filter soften water?
Not a standard sediment or carbon filter. Hardness is typically addressed with ion-exchange softening or another hardness-specific treatment.
Can hard water damage a water heater?
Scale can accumulate on heat-transfer surfaces and reduce efficiency over time, especially at higher hardness levels.
Does AquaTrust test hardness at the home?
Yes. Hardness is one of the common treatment conditions AquaTrust can screen during an in-home visit.
Can a softener also remove chlorine?
A standard softener is not designed for chlorine removal. Whole-home carbon filtration is the more relevant treatment category for chlorine taste and odor.
