How to Measure Mineral Salts in Bottled Water

Mineral salts comprise virtually all the dissolved solids found in drinking water, including bottled waters.

Salts impart electrical conductivity to water because they dissociate as free ions. The positively charged ions--or cations--in drinking water are principally calcium, magnesium, potassium and sodium; the negative ions--or anions--are principally bicarbonates and chlorides, nitrates and sulfates.

Instruments that measure conductivity are often used to test water for salt content, but they can only provide an approximation. An accurate measurement requires a determination of the weight of dissolved solids.

Things You'll Need

• Milligram electronic balance, capacity 50 grams
• Clean 100 ml and 10 ml beakers
• Clean 100 ml measuring cylinder
• Oven
• Thin glove or mitt
• Fine-tipped squirt bottle containing distilled water

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Instructions

• 1

  Electronic weight balance

  Weigh the 10 ml beaker to the highest precision. Record the weight and set it aside.

• 2

  Volumetric cylinder

  Measure exactly 100 ml of bottled water into the cylinder then pour the water into the 100 ml beaker.

• 3

  Beaker with blue liquid

  Place the beaker in the oven and set the oven to 100 degrees Celsius (212 Fahrenheit). Allow the water to evaporate until 3 to 5 ml remain--do not allow it to evaporate completely.

• 4

  Remove the beaker carefully from the oven, using the glove, and set it down to cool. Leave the oven on.

• 5

  Pour the water into the 10 ml beaker. Rinse the 100 ml beaker with 2 to 3 ml of distilled water and add the rinse to the 10 ml beaker. Repeat the rinse procedure, being careful not to exceed 10 ml in total.

• 6

  Place the beaker in the oven and allow the contents to evaporate completely.

  Increase the temperature to 180 degrees Celsius and leave for 24 hours. This will ensure that water is completely removed from the solids.

  Turn off the oven and allow the beaker to cool down.

• 7

  Remove the beaker from the oven. Weigh it and record the weight.

• 8

  Compute the concentration of dissolved mineral salts as follows:

  Weight of beaker containing dried sample - weight of empty beaker = weight of minerals.

  Weight of minerals x 10 = concentration of minerals in the units "grams per liter of water."

  Grams of minerals per liter of water x 1000 = milligrams of minerals per liter of water.