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How to Calculate Water Hardness?

Have you heard of the term “hard water”? Well, water contains a high amount of minerals that include calcium and magnesium. It also occurs in many various water sources across the world.

Although hard water does not cause illnesses, it can lead to various problems at home appliances or factories. For instance, it can destroy heavy machinery, thus leading to expensive repairs. It even forms chalky deposits on heaters or plumbing thus keeping soaps from creating suds quickly.

To handle this issue, you will have to treat the water. But before you start looking for a water softener; let’s show you how to calculate water hardness.

What is Water Hardness?

You can define water hardness as the number of dissolved minerals in the water. Usually, hard water contains a high amount of calcium and magnesium. When you wash your body with this water, you can feel its effects on your skin.

Depending on the amount of minerals, you might feel a filmy residue on your skin, especially after washing with soap. This feeling occurs because the soap reacts with the calcium in the water to produce a “soap scum.” As a result, you will have to use extra detergent or soap with hard water.

After washing your glassware in a dishwasher, you might discover some weird spots on them. Also known as hard water residue, this film has an ugly look. However, it does not pose any risk to your health.

As mentioned earlier, homes and businesses show concern about their water hardness. After all, when it is exposed to heat, the water forms a thick residue of calcium carbonate or limescale.

Limescale can damage machinery, increase your utility bills, and affect the efficiency of your water heater. It can also block your plumbing and give your coffee maker an ugly look.

To restore the coffee maker to its original look, people sporadically toss vinegar into the pot. Since it has acidic features, the substance works by charging the limescale. Next, the charged particles move towards the water molecules, thereby making the scum easy to wash off.

Does hard water have any benefits? Yes, it has offered vital minerals that perform functions in the human body. Experts even suggest drinking water as a way to increase the mineral content in your body.

What Does Temporary and Permanent Hardness Mean?

Temporary Hardness of Water

This form of hardness results from the occurrence of dissolved calcium and sodium bicarbonates in the water. You can remove this water hardness by tossing in some lime or calcium hydroxide (lime softening).

Permanent Hardness of Water

Unlike the type mentioned above, this hardness requires special treatment due to its sulfate and chloride ions. To tackle the stubborn particles, you will need an ion exchange resin or water softener.

You can also describe permanent hardness as the sum total of calcium and magnesium hardness in water. If you want to know how to calculate water hardness, you will need a specialized test kit.

How Does A Hard Water Calculator Work?

How Does A Hard Water Calculator Work

As you already know, the hardness of water comes in two forms – permanent and temporary. With a hard water calculator, you can find overall permanent hardness. The calculator uses the formula below:


The calcium and magnesium stand as the concentration of both elements stated as calcium carbonate.

These values stand as the molar mass of several related compounds.

  • CaC03 = 100,1 g/mol
  • Ca2+ = 40, 1g/mol
  • Mg2+= 24,3g/mol

The molar masses ratio can be expressed as:

  • MCaCo3/MCa = 100,1/40,1=2,5
  • MCaCo3/Mmg = 100,1/24,3 =4,1

This means that the overall permanent water hardness which equals CaCO3 can be determined with the formula below:

  • (CaC03) = 2,5 . (Ca2+) + 4,1 (Mg2+)

So if you looking for “how to calculate water hardness formula”, you can use the one above.

Steps to Determine the Carbonate Hardness in Water (CH)

Even if the full hardness in 1 depends on the number of cations, it can also depend on the amount of anions. The latter divides the carbonate hardness/ temporary hardness and permanent hardness.

  • Total Hardness TH =  CH  +  NCH

Carbonate hardness has a relationship with alkalinity:

  • CH in meq/L    =    [Alk in meq/L]
  • CH in °dH    =    809 × [Alk in meq/L]

Using water chemistry, alkalinity and carbonate hardness have similar meanings.

  • Carbonate Hardness CH = Alkalinity

With the program, you can calculate total and carbonate hardness while showing output tables as below.

How Can I Measure Hardness in Water?

A measure of water hardness comes with many units. These include grains per gallon, milligrams of calcium per liter, parts per million. You might use a German degree of hardness; however, this unit fits only fish tanks.

To determine the hardness, head to a water test lab with a water sample. Then, convert the results with water hardness measures. For instance, 35ppm = 35mg of dissolved minerals per liter of water.

How to Use Soap to Determine the Grains of Hardness in A Water Sample

For this test, you will need a small bottle with a fitted cover and water level mark. In its place, you can use the marked container in a water hardness testing kit. You will also need some dish soap and a measuring cup.

Now that you know how to calculate water hardness in ppm, fill the bottle (to the mark) with water. Pour a little soap and shake to create bubbles.

If you need to add more soap to notice any suds, this shows a high amount of dissolved salts. If you use less, then the water has a low amount of minerals.

While this test shows water hardness, it cannot offer precise readings. For accurate tests, get a water test kit. You can also get these items for free or affordable prices.

How to Measure Water Hardness with a Test Kit

If you want to have a perfect idea of the water hardness in a sample, use test strips that have special pads. You can even use these products to check if your water distiller or softener works well.

Apart from these devices, some instruments can also give readings on water hardness. Now let’s see how to calculate water hardness with both items.

Measuring Water Hardness with Instruments

With the help of a colorimeter, a white light beam moves through an optical filter. Normally, the screen sends a specific color of light to the photodetector for readings.

To know the amount of colored light taken in by a sample, you will have to confirm the difference between the amount of colored light sent by a blank and colored sample.

When using a colorimetric test, you discover that the quantity of absorbed light has a relationship with its concentration. You can even notice this fact on the meter.

Measuring Water Hardness with Test Strips

If you want to know how to measure water hardness with another tool, consider getting a test strip. These simple plastic items have thick pads on their surface. With these components, the strips can detect a particular ion and create a distinct color change.

When the test strip forms a color, it’s compared to a color chart. On this printed chart, you will find color reactions at different concentrations. You can get a reading by comparing the strip to a similar color. If you can’t find one, choose the hue closest to the color on the strip.

How to Calculate Water Hardness With Test Strips

Step 1. Select Your Water Source

For untreated water hardness: To know how to measure water hardness in water coming into your location, look for an outdoor faucet. You can also check a source that has not passed through a softener or distiller.

Avoid collecting water from a garden pipe as this channel might contain particles that can affect your readings. Allow the water to flow until it reaches a stable level, as this shows that you collected water from an outside source.

For Treated Water Hardness: To check if your water softener works well, look for a water source that extends from the softener or whole house water filler.

Remove the test strip from its packaging. Ensure that its sensing pad does not touch your skin as any contact can affect potential readings.

Step 2. Insert the Test Strip

Place the test strip into a clean glass filled with the water sample. Allow to sit for 2 seconds or as instructed by the kit’s manufacturer. To avoid inaccurate results, do not leave the test strip in water for an extended period.

Pull out the strip and shake to remove excess water. Continue waving until every water drop disappears. Overall, ensure the piece shows slight wetness.

In a horizontal position, hold up the strip for between 10 – 30 seconds. Within this time, the piece can show signs of a chemical reaction

Step 3. Read the water hardness

To know how to measure water hardness with a strip, compare the color of its test pad with the water hardness chart on its packaging. Most times, the colors displayed depend on the brand of your water testing kit.

If used properly, your treated water should have a hardness reading of 0. For untreated water, expect higher values of up to 425.

Wrap Up

Water contains dissolved minerals. But when they exist in large amounts, the water becomes hard. Such metals include magnesium and calcium.

The main types of hardness include permanent and temporary water hardness. To solve these problems, you might need:

  • Water softener or lime
  • You can use a bottle and soap test
  • for accurate results, invest in an affordable water testing kit

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1 thought on “How to Calculate Water Hardness?”

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