Testing Water Hardness

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Updated on Nov 19, 2013

Water, the major building block of life, sometimes has additives for health reasons. Hard wateris water that has a high amount of dissolved minerals, generally calcium carbonate or magnesium salts.This is not necessarily a bad thing—most water in our households has some degree of hardness. Water that is too hard often tastes weird to us, but so does completely soft water, because we are used to a certain amount of minerals in the water. Hard and soft water are both perfectly fine for our health.

Hard water, however, can be an issue for some households and businesses because it requires more soap and detergent to produce bubbles or a lather. Hard water also leaves much more soap scum and grime than soft water. Businesses and industrial operations often monitor water hardness because the calcium and magnesium salts can sometimes build up in pipes and block water flow, and eventually cause corrosion.

Find out what will happen as you add more Epsom salts to water.


  • Distilled water
  • Epsom salt
  • Labeling tape
  • 5 Cups of the same size
  • Teaspoon
  • Hand soap
  • Water hardness testing strips (can be found at places like Home Depot, Lowes)
  • Notebook and pen/pencil


  1. Fill each of the five cups with the same amount of distilled water.
  2. Label your cups. Your first cup will get no salt—this is the control. The last cup will get four teaspoons of salt.
  3. Skipping the first cup, fill your cups with 1, 2, 3 and 4 teaspoons of salt, respectively. Be sure to label correctly.
  4. Stir each cup until all the salt is dissolved.
  5. Put a small amount of hand soap on your hands and wet them with one of thewater samples. Record your observations on how easy it is to produce bubbles. Which water samples are the hardest based on this test?
  6. Use the strips in the hardness testing kit to rank the water samples from hardest to softest. Does this match up with your bubble test?


The water with the highest amount of dissolved salts will be the hardest.


Epsom salt is a common name for magnesium sulfate. When mixed with water, it separates into Mg2+, a component of water hardness, and sulfate anion, SO4-2. The more salt you put in the water, the higher its dissolved magnesium concentration will be, causing the water to be harder.

The harder the water, the harder it will be to produce bubbles. Cup number 5 will be the most difficult to turn into a later on your hands, and may even leave your hands feeling sticky and dirty from the soap scum.

Going Further

Compare your results to water samples from your house tap water or filtered water.

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