Water Hardness

What is my water hardness?

Depending on where you live it can range from 1 to 150.

If you want to know the water hardness in your area, please call WBUD to find out.

What is Hardness?

Hardness in water refers to specific minerals that consume soap and cause scaling in water heaters and boilers. The more minerals, the harder the water. Soft water refers to the absence of these minerals.

The term hardness comes from an expression of how difficult or "hard" it is to wash clothes with the water. When soap is mixed with hard water, these minerals combine with the soap and form a precipitate, or a solid. This decreases the cleaning efficiency of the soap and forms soap scum. As more soap is added, solids continue to form until the minerals are depleted. When the minerals are no longer available, the soap forms a lather and works as a cleaning agent.

The minerals that precipitate with soap are polyvalent cations such as calcium, magnesium, iron, manganese, and zinc. The concentration of calcium and magnesium in natural waters generally far exceeds that of any other polyvalent cation. Therefore, hardness is generally considered to be the concentration of calcium and magnesium in water.

Carbonate and Non-Carbonate Hardness: Hardness can be classified as carbonate and non-carbonate hardness. Carbonate hardness refers to calcium and magnesium bicarbonate. When calcium bicarbonate is heated, solid calcium carbonate forms. This is the primary cause of scale formation in water heaters and boilers. Non-carbonate hardness is caused primarily by calcium and magnesium nitrates, chlorides, and sulfates.

Hardness is removed from water systems by precipitation or ion exchange. The treatment method varies depending on the relative amounts of carbonate vs. non-carbonate hardness.

The amount of carbonate vs. non-carbonate hardness can be found by measuring alkalinity. If the alkalinity is equal to or greater than the hardness, all of the hardness is carbonate. Any excess hardness is non-carbonate hardness.

Hardness is typically reported in terms of mg/L as CaCO3 or gpg as CaCO3. Because alkalinity is also reported as CaCO3, the results of the two tests can be compared directly.

How can I measure Hardness in water?

Hardness is most commonly measured by titration with an EDTA solution. A titration involves adding small amounts of a solution to a water sample until the sample changes color. You can titrate a sample for total hardness using a buret or test kit. You can also measure calcium hardness separately from magnesium hardness by adjusting the pH and using different indicators.

Hach Drop Count Test Kits for total hardness use a dropper to add the EDTA solution to the sample. Test kit model HA-71A, which uses ManVer indicator, works best for natural water samples, especially when iron or manganese is present, or when alkalinity is high. Test kit models 5-B, 5-EP, and 5-EP/MG-L, which use UniVer reagent, work best for industrial samples that may have high concentrations of metals such as copper. Other kits are available for measuring calcium and magnesium hardness separately.

Kits using the Digital Titrator can measure hardness concentrations more accurately than drop count titration kits. This is because the Digital Titrator dispenses the EDTA solution in very small increments. Kits using the Digital Titrator use the ManVer indicator.

Test strips are also available for measuring hardness. A color develops on the strip and the strip is matched to a chart. The charts shows colors for concentrations of 0, 25, 50, 120, 250, and 425 ppm, or 1, 1.5, 3.7, 15, and 25 gpg. Use test strips when a general range for hardness is sufficient. Test strips should not be used when an exact hardness concentration is required.

When you need to measure hardness in extremely soft water, where the concentration is expected to be less than 4 mg/L as CaCO3, use a colorimeter such as the DR/820, DR/850, or DR/890 Colorimeter, or a spectrophotometer such as the DR/2400, DR/2500, or DR/4000 Spectrophotometer.

Calcium can also be measured using an ion-selective electrode, such as the model ISE25Ca Calcium Electrode made by Radiometer Analytical. An electrode is the best method to use when color or turbidity in the sample interferes with titration or colorimetric methods.

What concentration of Hardness is considered hard or soft?
There is no universal agreement on what exact concentrations are considered hard or soft. The following table shows the classifications used by the U.S. Department of Interior and Water Quality Association. Other organizations may use slightly different classifications.

0 - 17
0 - 1
Slightly hard
17 - 60
1 - 3.5
Moderately hard
60 - 120
3.5 - 7.0
120 - 180
7.0 - 10.5
Very Hard

The hardness concentrations shown above are in terms of mg/L or gpg as CaCO3.