How to Measure Water Hardness

Co-authored by Hunter Rising

Last Updated: January 20, 2021 References

Water hardness refers to the amount of calcium and magnesium in your water supply. Hard water in your home can leave spots on your dishes, make you use more soap, and cause buildup in your pipes. If you have an aquarium, the hardness can also affect the chemical balance of your tank. You can use regular dish soap as a rough test, but you can also use a test meter or test kit for a more accurate reading. Once you test your water, you’ll be able to take the next steps to soften it!

Method 1

Method 1 of 4:

Checking for Water Hardness with Soap

1
Fill a bottle with 1 ¹⁄₂ c (350 ml) of water. Set up a small work area near a kitchen sink so you can easily access water and soap. Use a clear plastic or glass bottle that has a cap so it doesn’t spill out. Pour 1 ¹⁄₂ cups (350 ml) of cold tap water into the bottle and leave the cap off for now.^{[1]
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- You can reuse an old water or soda bottle as long as you rinse it out first.
- If you don’t have a bottle, use a clear drinking glass for your test.
2
Add 10 drops of liquid dish soap to the bottle. Carefully squeeze the liquid dish soap into the water, counting each drop as you add it. Be careful not to squeeze too hard or else you won’t be able to read your test results. Once you add the 10th drop to the water, wipe the edge of the soap bottle so it doesn’t drip anymore.^{[2]
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- Any liquid dish soap will work for this test.
- If you want to be more precise, use a pipette to add your soap to the bottle.
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3
Put a cap on the bottle and shake it vigorously. Screw the cap onto the bottle so it forms a tight seal and doesn’t leak. Shake the bottle up and down to combine the soap and water until it’s thoroughly mixed. After a few seconds, set the bottle down and let it settle for another 5 seconds.^{[3]
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- If you didn’t have a bottle, use a stir stick to mix together the soap.
4
Stop your test if the water is sudsy. Observe the water inside the bottle to see if there is a 1 in (2.5 cm) layer of bubbles on the surface of the water. If there is, then you have soft water and you don’t need to take any further action. If your water looks cloudy and doesn’t have suds forming on top, then it’s considered hard water.^{[4]
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Tip: Repeat the test with a bottle of purified water to see the difference. The purified water will start to form suds after the initial 10 drops since it has calcium and magnesium deposits filtered out so it is very soft.
5
Continue adding 2-3 drops of soap at a time if the water is not sudsy. Open your bottle and put another few drops into the water before capping it again. Keep track of the number of drops you add so you can estimate your water hardness later. Shake the bottle for a few seconds to combine the soap and water before observing it again. If there are still no suds, keep adding drops until you see a layer of bubbles on top that’s at least 1 inch (2.5 cm) tall.^{[5]
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- Hard water has mineral deposits which make it harder to form bubbles, so it takes more soap for it to create suds.
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Note that your water is hard if you had to add more than 20 drops of soap. If your water started sudsing after the first 10-20 drops, then you have soft water and don’t need to make any changes. If you used 20 or more drops of soap, then you have hard water and may need to soften it to help protect your appliances and pipes from buildup. Anything over 50 drops is considered very hard and may cause the most buildup.^{[6]
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- Water hardness does not affect your health, but it does affect your appliances and how much soap you use.

Method 2

Method 2 of 4:

Using a Test Meter

1
Hold the “On” button down until the display lights up. Water hardness test meters detect the number of solids dissolved in your water. Find the “On” button near the meter’s display and press it down for a few seconds. After 2-3 seconds, the display will light up and read “0.0” so you can start using the meter.^{[7]
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- You can buy a water hardness meter online or from hardware stores.
2
Dip the end of the test meter into a cup of cold tap water. Take the plastic cap off of your test meter to uncover the notched end used to test the water. Fill a small cup halfway with water so you’re able to submerge the end of the meter. Put the notched end of the meter into the water completely so it can measure the hardness.^{[8]
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- Be careful not to submerge the display since you may damage the meter.
3
Check the reading on the meter’s display to determine the water hardness. While the end of the meter is still submerged, check the number listed on the display. The meter will list the hardness of your water in parts per million so you can determine how soft it is. If you have a reading that’s 60 ppm or higher, you have hard water and should make adjustments to preserve your pipes and appliances.^{[9]
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- Press the “Hold” button on your meter if it has one so you can pull the meter out of the cup without the display changing.
- Be sure to rinse and dry your test meter between different water samples so your readings stay accurate.

Method 3

Method 3 of 4:

Getting Detailed Results with Test Kits

1
Buy hard water test strips from your local hardware store. Hard water test strips have a chemical in them that reacts with the minerals in your water. Find a pack of hard water strips in the plumbing section of a hardware store or online so you can test your water. Make sure the strips are for tap water and not for aquariums since the reading will be slightly different.
- You may be able to get a free testing strip from water treatment services or websites that sell water softeners.
- You can also buy test strips that also check for chlorine, pH, and alkalinity.
2
Dip the testing strip in cold water for 1 second so the end changes color. Hold the end of the test strip that doesn’t have the colored square on it. Fill a small bowl with cold tap water and dunk the end of the test strip in it. As soon as you wet the square on the end of the test strip, immediately pull it out of the water and shake off any drops.^{[10]
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- If you have test strips that check other chemicals in your water, such as alkalinity or pH, then submerge all of the squares on the end.
Tip: Try testing water from multiple sinks in your home to see if the water hardness varies.
3
Compare the color of the test strip to the chart on the packaging. Remove the chart from the package of test strips or find it on the side of the package. Hold the square on the test strip up to the chart on the test strip and match the colors as closely as you can. The chart will tell you how many “grains” of hardness or parts per million (ppm) your water has.^{[11]
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- Usually, a dark blue means you have very hard water that’s about 24 grains, or 400 ppm.

Method 4

Method 4 of 4:

Determining Water Hardness in an Aquarium

1
Buy a test kit for carbonate hardness and general hardness. Unlike regular tap water where you only check the general hardness (GH), you need to test aquariums for their carbonate hardness (KH) as well. Look at pet stores or online for a test kit that contains solutions for both KH and GH so you can get a complete understanding of your aquarium’s chemical balance.
- KH measures the alkalinity of the tank from carbonate deposits in the water, which is harmful to fish in large quantities.
- GH measures the amount of calcium and magnesium in the water.
- If you have a saltwater aquarium, make sure you get a test that can handle the amounts of alkalinity in the tank.
2
Fill 2 test tubes with 1 tsp (4.9 ml) of aquarium water each. Your kit will come with 2 test tubes in it so you can fill them both with water and run each test at the same time. Draw out some of the water from your aquarium and squirt it into the test tube up to the marked line, which will be about 1 teaspoon (4.9 ml). Once you fill the test tube, set it in a holder so it doesn’t tip over and spill.
- Make sure the test tubes have the same amount of water or else the test won’t be as accurate.
3
Place a drop of the KH solution in the first test tube. Open the bottle of the KH solution and carefully hold the tip over the edge of one of your test tubes. Squeeze the sides of the bottle lightly until a drop comes out into the test tube. Be careful not to squeeze too hard or else you may need to start your test over.^{[12]
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Put a cap on the test tube and shake it. Take the test tube that you just added the KH solution to and cap it so it has a tight seal. Flip the test tube over and swirl it around to mix the solution into the water. After about 5 seconds of mixing the solution, it will turn dark blue instead of clear.^{[13]
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- The test kit you buy will come with caps for the test tubes.
5
Continue adding 1 drop at a time until the solution turns yellow. Uncap the test tube and add another drop of the KH solution into the water. Keep track of each drop so you can compare the number to the chart in the kit. Cap the test tube and swirl it around to mix the solution after each drop before looking at the color again. Once the solution turns a bright yellow color, stop adding drops.^{[14]
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- Write down the number of drops on a piece of tape and wrap it to the test tube if you don’t want to forget.
Tip: Hold the test tube in front of a white sheet of paper if it’s hard to notice any color changes.
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Compare the number of drops you used to the chart in the kit instructions. Find the table or conversion chart provided in the test’s instruction manual or inside the box. Find the number or range that matches how many drops you used to find out the alkalinity of your tank. The more drops you had to add to the test tube, the more alkaline your water is, which may mean you need to do a water change.
- The KH will either be listed in degrees of carbonate hardness (dKH) or parts per million.
- The KH and alkalinity affect how well the aquarium water neutralizes acids so your tank’s pH is unaffected.
7
Repeat the test with the GH solution in the second test tube. Put a drop of the GH solution in the second test tube of aquarium water before capping it and shaking it. The water in the second test tube will turn orange after the first drop, but turn green as you add more drops. Continue putting in drops of the GH solution and counting each one until the water turns green. Compare the number of drops you used to the chart on the packaging to determine how hard the water is.
- Different species of fish prefer different levels of hardness, so the overall measurement depends on what type of fish you’re keeping.
- The GH is usually measured in parts per million.

Warnings

Hard water can lead to buildup and mineral deposits in your pipes, so be sure to get a water softener to prevent any accumulation.

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