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How do you measure the hardness of water?

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Quick Answer

To measure the hardness of water, either titrate a sample of the water with an ethylenediaminetetraacetic acid, or EDTA, solution or use a test strip kit. Hardness refers to the amount of minerals in the water, such as calcium, magnesium and iron. When soap is added to the water, it binds to the minerals and forms a solid.

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Full Answer

Use the following steps to measure the hardness of water:

  1. Gather the materials
  2. Gather together the materials needed to test the water, such as a titration kit or test strip kit. Test strips are useful when only a general range is needed. When the specific level of hardness is required, use a titration kit.

  3. Take a water sample
  4. Place a sample of the water being tested in a container to make it easier to add the titration solution.

  5. Add the solution
  6. Take a dropper and add small amount of the titration solution to the water sample until it begins to change color. If using a test strip, add the strip to the water sample and allow it to change color.

  7. Compare to the chart
  8. Compare the color to the chart provided by the kit. Hardness is typically measured in milligrams per liter as CaCO3. Water that has a reading of 17 mg/L or more is considered to have some level of hardness.

To measure water hardness using the soap method, fill a glass bottle that can be sealed with 12 ounces of test water. Add drops of dish soap one at a time, sealing the bottle and shaking it after each drop. Keep adding more soap drops until soap suds form when shaking. The more soap it takes to form suds, the harder the water must be. Under 20 drops of soap means the water is soft or slightly hard. Water is medium-hard at 20 to 40 drops of soap, and very hard above 40.

Hard water causes calcium and magnesium buildup on plumbing fixtures and makes washing more difficult. Fix hard-water problems permanently by installing a water softener. Stores sell many types of water softeners, including the common two-tank system.

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