Measuring Water Hardness

Hard water is water that has high mineral content (as opposed to "soft water"). Calcium is the most common mineral associated with water hardness. While hardness is not generally a health hazard it can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment. In domestic settings, hard water is often indicated by a lack of suds formation when soap is agitated in water, and by the formation of limescale in kettles and water heaters. Wherever water hardness is a concern, water softening is commonly used to reduce hard water's adverse effects.

hardness map

Calcium hardness in pools and spas can often present problems for the pool owner. Low calcium hardness can result in corrosion of metal equipment or erosion of plaster surfaces and tile grouting. This can lead to the need for resurfacing. High calcium hardness results in scale formation on the pool surfaces as well as scaling in the pipes, plumbing and filter. In extreme cases the water becomes dull and cloudy with the calcium precipitating out into the water rather than onto a surface. High calcium levels will also impact swimmers, causing irritated eyes in particular.

Although water hardness usually measures only the total concentrations of calcium and magnesium, iron can also be present at elevated levels. The presence of iron characteristically creates a brownish (rust-like) color to the calcification, instead of white (the color of most of the other compounds).

Types of Water Hardness

Temporary Hardness

Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate). However, unlike the permanent hardness caused by sulfate and chloride compounds, this "temporary" hardness can be reduced by the addition of lime (calcium hydroxide) through the softening process of lime softening.

Permanent hardness

Permanent hardness is hardness (mineral content) that cannot be removed. Ions causing permanent hardness of water can be removed using a water softener, or ion exchange resin.

Total Permanent Hardness = Calcium Hardness + Magnesium Hardness

The calcium and magnesium hardness is the concentration of calcium and magnesium ions expressed as equivalent of calcium carbonate.

Hardness can be quantified through instrumental analysis, an individual test kit, or through the use of test strips specifically formulated for making these measurements.

 

How to Measure Water hardness

Instruments

A colorimeter passes a white light beam through an optical filter which transmits only one particular color or band of wavelengths of light to the photodetector, where it is measured. The difference in the amount of colored light transmitted by a colorless sample (blank), and the amount of colored light transmitted by a colored sample, is a measurement of the amount of colored light absorbed by the sample. In most colorimetric tests, including hardness, the amount of colored light absorbed is directly proportional to the concentration and is reported by the meter.

Test Strips

Test strips are typically produced from plastic, with chemically impregnated pads on the end. These pads are designed to react with specific ions and produce a specific color change. Once a test strip is reacted and a color is developed, the strip is then compared to a printed color chart. The color chart is specifically designed to represent color reactions at various concentrations. Matching the strip to the closest color match produces a concentration reading.

 

Suggested Items for Testing Hardness

Hardness Test Strips

Iron, pH, and Hardness Test Strips

Iron, pH, and Hardness Test Strips

Order Code: 2980
Applications: Drinking Water

These test strips test for Iron, pH, and Hardness levels. Range and sensitivity is Iron - 0, 0.3, 0.5, 1, 3, 5 ppm, pH - 4, 5, 6, 7, 8, 9 10, and Hardness 0, 50, 100, 200, 400 ppm.


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298149

Hardness Low Range Test Strips

Order Code: 2981
Applications: Drinking Water, Industrial Water Boiling and Cooling, Laundry and Sanitation, Water and Wastewater

The Insta-Test Low Range Hardness test strips are a convenient way to test Hardness levels in water for fast results. Range and sensitivity is 0, 30, 60, 120, 180 ppm.


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2933

Insta-Test 6-Way Drinking Water Test Strips

Order Code: 2933-G
Applications: Drinking Water

These test strips test for free and total chlorine, pH, hardness, nitrate, and nitrite.


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Hardness Test Kits

7246-02

Total Hardness Test Kit

Order Code: 7246-02
Applications: Industrial Water Boiling and Cooling, Water and Wastewater

This kit tests for Total Hardness using the Dropper Bottle Method. All results are as CaCO3. Range/sensitivity is 1 drop = 2, 5, or 10 ppm CaCO3.


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4482-dr-lt-015

Total Hardness Test Kit

Order Code: 4482-DR-LT-02
Applications: Environmental Education, Food and Beverage, Industrial Water Boiling and Cooling, Laundry and Sanitation, Water and Wastewater

This kit tests for Total Hardness by using the Direct Reading Titrator Method. All results are as CaCO3. Range/sensitivity is 0-200 ppm/4 ppm CaCO3.


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3609-01

Calcium Hardness in Fresh or Salt Water Test Kit

Order Code: 3609-01
Applications: Environmental Education, Food and Beverage, Industrial Water Boiling and Cooling, Laundry and Sanitation, Water and Wastewater

This kit tests for Calcium Hardness in fresh or salt water. Includes inhibitors to eliminate metal interferences. All results are as CaCO3. Range/sensitivity is 0-200 ppm/4 ppm CaCO3, 0-2,500 ppm by dilution.


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Alkalinity & Calcium Hardness Test Kit

Alkalinity & Calcium Hardness Test Kit

Order Code: 3583
Applications: Pool and Spa

The Alkalinity and Calcium Hardness TesTabsĀ® test kit uses one tablet per test factor which is added to a test tube of water sample to develop a color. Sample water is added performing a back titration until an endpoint color change occurs. The results are read directly from the test tube which measures Alkalinity and Calcium Hardness from 60 to 400 ppm. The kit includes simple to read instructions, 30 TesTabsĀ® tablets, a water sample bottle along with a preprinted test tube with Alkalinity and Calcium Hardness levels.


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Instruments

ColorQ Pool 4 Photometer

ColorQ Pool 4

Order Code: 2055
Applications: Pool and Spa

The ColorQ Pool 4 measures four basic pool and spa tests, Free Chlorine (0 to 10 ppm); Total Chlorine (0 to 10 ppm); Bromine (0 to 22 ppm) and pH (6.5 to 8.5 pH). As a bonus, the ColorQ Pool 4 can also measure Total Alkalinity, Calcium Hardness, and Cyanuric Acid with optional reagents sold separately. The photometer is easy to use and features economical liquid reagents for 144 tests.


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2056newcase

ColorQ PRO 7

Order Code: 2056
Applications: Pool and Spa

The unique, multi-test ColorQ pool and spa hand-held photometer reads SEVEN test factors (Free Chlorine, Total Chlorine, Bromine, pH, Alkalinity, Calcium Hardness, and Cyanuric Acid) directly on a digital display.


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2064t

ColorQ PRO 7 Plus

Order Code: 2064
Applications: Pool and Spa

The ColorQ PRO 7-PLUS handheld professional pool photometer directly measures the seven primary tests of Free Chlorine (DPD), Total Chlorine (DPD), Bromine (DPD), pH, Alkalinity, Calcium Hardness, and Cyanuric Acid directly on a digital display.


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2058t

ColorQ PRO 11

Order Code: 2058
Applications: Pool and Spa

The ultimate on-site hand-held pool and spa photometer. It measures eleven pool & spa tests directly on a digital display. Test factors include Free Chlorine, Total Chlorine, Bromine, pH, Alkalinity, Calcium Hardness, Cyanuric Acid, Iron, Copper, Biguanide, and Biguanide Shock.


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1910

SMART 3 Colorimeter

Order Code: 1910
Applications: Industrial Water Boiling and Cooling, Water and Wastewater

The compact SMART3 Colorimeter is ideal for water analysis in the field or in the lab. Easy to use software allows the analyst to choose a test factor from over 75 pre-programmed calibrations for LaMotte reagent systems.


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