How to understand water hardness test results

Written by theresa wellwood
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How to understand water hardness test results
Water described as "hard" is high in dissolved minerals, specifically calcium and magnesium. (medical test image by JASON WINTER from

Hard water is not a health hazard, but dealing with hard water in the home can be a nuisance. Laundry can become stiff, water vases encrusted with minerals, and bathing in hard water can leave a sticky film on the skin. The hardness (calcium and magnesium concentration) of water can be tested with a water testing kit. Water hardness is more accurately tested with a laboratory test. Water hardness can be managed with packaged water softeners or with a mechanical ion exchange softening unit.

Skill level:

Things you need

  • Water test kit

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  1. 1

    Acquire a water hardness testing kit from a testing supply company. Follow the directions on the water hardness testing kit.

  2. 2

    Read the results. The hardness of your water will be reported in grains per gallon, milligrams per litre (mg/l) or parts per million (ppm). One grain of hardness equals 17.1 mg/l or ppm of hardness.

  3. 3

    Interpret the results. water hardness is classified by the U.S. Department of Interior and the Water Quality Association as follows:

    Soft : 0 - 1 grains/gal

    Slightly hard: 1 - 3.5 grains/gal

    Moderately hard: 3.5 - 7.0 grains/gal

    Hard: 7.0 - 10.5 grains/gal

    Very Hard: 10.5 grains/gal & over

  4. 4

    Assess your options. If your water has a water hardness of 7.0 grains/gal or more, you may want to soften it. There are two ways to soften your water: packaged water softeners and mechanical water softening units.

Tips and warnings

  • Softened water is not recommended for watering plants, lawns, and gardens because of its sodium content.

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