Water Hardness Testing and Solutions

Industries That Require Hardness Monitoring

Drinking Water Industry

Excessive hardness of finished water released in the distribution system may cause scaling and if the water is too soft, it can cause corrosion of the pipes. Thus, leaching out lead and copper which may lead to violation of the lead and copper rule (LCR).

Wastewater

During sludge digestion, monitor hardness to optimize efficiency. Soap biodegradation and oxygen uptake by activated sludge are affected by elevated hardness concentrations.

Pool and Spa Water Testing

Water that is too "hard" can cause scaling, deposits of calcium carbonate. "Soft water" will corrode pipes and surfaces inside the pool, which contain calcium (like pool plaster) and other minerals.

Power Industry

Water hardness can cause scaling in water heaters and boiler tubes. Therefore, it is crucial to monitor and remove all salts, especially those causing hardness.

Chemical Manufacturing Industry

Monitor incoming water for mineral content in order to properly adjust product water quality and sensory factors. Monitor the performance of water softening systems to avoid scaling and assess the load on reverse osmosis systems. Continuous monitoring of boiler/cooling water (leaving the condenser) helps to detect minute and fluctuating levels of hardness that can cause scaling in piping, condensers and dryers over time. This allows operators to manage hardness levels, preventing damage and lost revenue due to downtime.

Food Manufacturing Industry

Monitor and manage total hardness to optimize boiler and cooling tower feed water. This minimizes chemical usage, prevents corrosion/scaling and protects plant equipment.

Mining Industry

Water is essential to metal and mining operations, but the industry is seldom the only consumer of water near extraction or processing sites. By monitoring and treating source water, mining companies not only ensure their own quality standards are met, but they also can contribute to the health of communities, agricultural resources and wildlife ecosystems in the process. Whether obtained from groundwater or precipitation, oceans or lakes, rivers or streams, through commercial or municipal supply—the water utilized in mining is interconnected with the water cycle of the entire region.

Pulp and Paper Industry

Monitor total hardness in water supplies to guard against in-plant corrosion and/or scaling, as well as effects of high hardness on the product quality.

Beverage Industry

Hardness of the water used to make beverages may affect their organoleptic properties.

How is Water Hardness Measured?

Titration

Hardness is commonly measured by colorimetric titration with an EDTA solution. A titration involves adding indicator and then titrant solution in small increments to a water sample until the sample changes color. You can titrate a sample for total hardness using a burette or use a water hardness test kit. You can also measure calcium hardness separately from magnesium hardness by adjusting the pH and using different indicators.

Drop Count Test Kits

This hardness test uses a dropper to add the EDTA solution to the sample and the drop counts are proportional to the water hardness. Total hardness test kit model HA-71A, uses ManVer ^® indicator and 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 test kits are available for measuring calcium and magnesium hardness separately.

Total Hardness, Model 5-B

Total Hardness, Model 5-EP

Total Hardness, Model HA-71A

Digital Titrator

Kits using the digital titrator can measure hardness more accurately than drop count titration kits. This is because the digital titrator dispenses the EDTA solution in very small increments with higher precision. Hardness test kits with digital titrator use the ManVer ^® indicator.

Hardness (Total & Ca), Model HAC-DT

Hardness (Calcium & Total Sequential) LR Reagent Set

Hardness (Calcium & Total Sequential) HR Reagent Set

Test Strips

When the water hardness test strip is dipped in a water sample, a color develops on the strip and the strip is matched to a chart. The chart shows colors for concentrations of 0, 25, 50, 120, 250, and 425 ppm, or 1, 1.5, 3.7, 15, and 25 gpg. Use the test strips when a general range for hardness is sufficient. Test strips should not be used when an exact hardness value is required.

Total Hardness, 0-425 mg/L

5 in 1 Test Strips

Colorimetry or Spectrophotometry

Use a colorimeter or a spectrophotometer when you need to measure hardness of extremely soft water, where the concentration is expected to be less than 4 mg/L as CaCO ₃ (calmagite method).

Benchtop/Portable:

Calmagite Reagent Set

Use a spectrophotometer when you need to measure ultra-low hardness in water, where the concentration is expected to be less than 1 mg/L as CaCO ₃ (chlorophosphonazo method).

Benchtop:

Chlorophosphonazo Reagent Set, Bulk Solution

Chlorophosphonazo Reagent Set, Solution Pillows

Use a spectrophotometer to measure higher ranges of total, Ca and Mg hardness.

Benchtop:

TNT869 Total Hardness (20-350 mg/L)

TNT849 Magnesium (0.5-50 mg/L)

Electrode

Calcium can also be measured using an ion-selective electrode, such as the Radiometer ISE25Ca or the 9660C Calcium Ion Selective Electrode (ISE). An electrode is the best method to use when color or turbidity in the sample interferes with colorimetric titration or spectrophotometric methods.

Benchtop:

AT1000

AT1000 Titration Application Pack Ca & Mg Hardness

AT1000 Titration Application Pack for pH/Alkalinity & Hardness

ISECa

Online Analysis

Online analyzers allow for continuous hardness monitoring. These instruments can activate alarms or control chemical feed pumps when the hardness concentration reaches a selected level.

EZ Series Hardness Analyzers

Water Softening

To reduce undesirable hardness, water must be softened. Softening methods typically fall into two main categories:

Ion Exchange Softening Process

This process exchanges cations causing hardness with non-hardness-causing cations, typically sodium, using either natural or synthetic ion-exchanging matrix, e.g. resin. For example, naturally occurring matrices include greensands and zeolites. Different ion-exchange resins (or matrices) possess varying properties. Synthetic materials tend to have a higher exchange capacity, so they are better for removing higher levels of hardness. Resins using hydrogen as the cation are commonly referred to as demineralizers and usually are comprised of both cation and anion-exchange resins to maintain neutral pH. For health reasons, it is important to note that sodium-based resin will increase the sodium levels in the treated water. This may also provide interference to some ULR hardness methods.

Once the exchange capacity of a resin has been exhausted, most can be regenerated so it is important to monitor effluent hardness to determine when the column needs regeneration. In this two-step process, first the unit is flushed to remove sediment, and then a brine solution is circulated through the resin at certain conditions to replace the accumulated calcium and magnesium ions with the cation used for softening originally.

Advantages

• The method does not appreciably affect other properties of the water, such as pH.
• Hardness causing cations other than magnesium and calcium are also removed by this process.
• This process can reduce hardness to near zero.

Disadvantages

• High levels of iron or manganese in the water can foul the ion exchange resin.
• Sodium resins can elevate sodium levels in finished water and cause interference to some ULR methods for hardness monitoring.
• High solids can foul resin beds, causing additional expense.

Precipitation Softening Process

Precipitation is typically accomplished with the lime-soda process. When lime is added to hard water, it causes a reaction with the carbonate hardness present producing solids that then must be removed from the water. Lime and soda ash can be used together to remove both carbonate and non-carbonate hardness. Compared with calcium precipitation, magnesium precipitation requires twice the amount of chemical additive and generates twice the amount of sludge that must be removed. Excess carbon dioxide must be removed prior to softening because it can impede lime precipitation.

Advantages

• This process may remove excess iron and fluoride.
• Due to the high pH, bacteria and viruses may be removed by this process.
• With proper control, corrosivity and scale formation can be controlled with this method.

Disadvantages

• It produces a considerable amount of sludge that requires disposal.
• Operation and chemical costs are high.
• The addition of soda ash may affect sodium levels in the water.
• Recarbonation, or the reintroduction of carbon dioxide, must be performed after softening to lower pH, to remove excess lime and to encourage the precipitation of any remaining calcium carbonate.
• This process cannot reduce hardness to zero.
• This process requires a high degree of operator skills to control.

Frequently Asked Questions