Hard well water: what your hardness number means
Hardness isn't a health concern. It's calcium and magnesium, and it causes scale on fixtures and water heaters. Over 180 mg/L (about 10.5 grains per gallon) is very hard.
- US (EPA)
- No limit.
- Ontario
- Operational guideline 80 to 100 mg/L for treated systems; not a health limit.
What it is
Hardness comes from limestone and other minerals the water passes through. Labs report it as mg/L of calcium carbonate, or in grains per gallon. One grain per gallon equals 17.1 mg/L.
What your number means
- Within limits0 to 60 mg/L
Soft.
- Within limits61 to 120 mg/L
Moderately hard.
- Worth a look121 to 180 mg/L
Hard. Some scale.
- Worth a lookAbove 180 mg/L
Very hard. Scale on fixtures, shorter water heater life.
What to do
- Decide whether scale bothers you. There's no health reason to soften.
- If you soften, keep one unsoftened tap for drinking, because softeners add sodium.
- Size the softener from your hardness and iron numbers.
How often to test
With a full panel every 3 to 5 years.
Common questions
Is hard water bad for you?
No. Calcium and magnesium are natural minerals and not a health concern in drinking water.
How do I convert grains per gallon to mg/L?
Multiply grains per gallon by 17.1.
Sources: Ontario: testing and treating private wells. Limits checked October 2026.