How to Test Water Hardness at Home

What you're measuring

A hardness test measures calcium and magnesium, the two minerals that make water hard. Results come in grains per gallon (gpg) or milligrams per liter (mg/L, the same as ppm). One gpg is about 17 mg/L, so divide a ppm reading by 17 to get grains.

If you're on a private well, hardness is only one line on the report. Iron matters just as much, because red, oxidized iron clogs softener resin and Penn State says it should be filtered out before softening. Test both before you buy equipment. The annual safety tests for a well (bacteria and nitrate) are a separate job, covered in our well water testing guide.

Your options, from rough to exact

The soap shake test (no kit)

Fill a clear bottle about a third full with tap water, add a few drops of plain liquid soap (not detergent, which lathers in anything), cap it and shake hard. Lots of suds and clear water underneath means soft. Thin suds and cloudy, milky water means hard. It won't give you a number, but it will tell you whether to bother with a kit.

Test strips

Strips are the cheapest hardness test kit and the easiest to use. Read the instructions on your bottle, because dip time and read time vary by brand. In general:

1. Run the cold tap for a bit and fill a clean glass.
2. Dip the strip for the time the label says, shake off the extra, and wait.
3. Compare the pad to the color chart in good daylight, not under a yellow kitchen bulb.

Strips are good at telling soft from very hard. They're weaker in the middle of the range, where two neighboring colors look alike. If your result falls between two blocks, call it the higher one and confirm with a drop kit before you program a softener.

Drop-count titration kits

This is a common field method for water treatment techs. With the Hach Model 5-B, you add a reagent that turns the sample red or pink if hardness is present, then add titrant one drop at a time until it turns blue. Each drop equals 1 gpg, so the drop count is your hardness. One kit does about 100 tests.

Count slowly and swirl after every drop. The color change is sharp once you've seen it, and rushing past it is the usual way people get a reading a few grains high.

Lab tests

Penn State recommends an independent lab test, which isn't expensive and protects you from being oversold. Softener dealers often test for free. That number is a useful second opinion, but it shouldn't be the only one you have. On a well, the CDC says to use a state-certified laboratory, and your county health department can point you to one. Order iron, manganese and pH on the same sample.

Where and how to take the sample

• Use a cold tap. Hot water can drop some hardness out as scale in the heater and read low.
• Test before the softener. If you already have one, take the sample from an outdoor spigot or another tap that bypasses it. That's your raw hardness, the number the softener needs.
• Test after the softener too. A kitchen tap on softened water should read at or near zero. If it doesn't, the softener isn't regenerating or is out of salt.
• Use a clean container. Rinse it with the water you're testing first.

Reading your results

Penn State's scale:

The number that matters for most people is 7 gpg. Penn State says water below 7.0 gpg probably won't cause major scaling or soap film, so a softener there is a comfort choice, not a need. Above it, scale on fixtures and in the water heater becomes a real cost.

Next steps

• Under about 7 gpg: Clean scale with vinegar and flush the water heater now and then. Most homes stop here.
• Over about 7 gpg: Read do I need a water softener? and use your number with what size water softener do I need.
• Already have a softener: Enter your raw hardness in the control. Our water softener hardness setting guide shows how.
• Orange stains as well as scale: Get an iron test. See iron in well water.