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Measurement of Alkalinity in Water

Alkalinity is a measure of the capacity of water to neutralize acids. This is known as the buffering capacity of water, or the ability of water to resist a change in pH when acid is added.

The properties of water are is easily influenced by alkalinity, making it an important and widely used test.

Alkalinity in water (with a pH of 7.0 or higher) is caused primarily by the presence of dissolved acid-neutralizing substances (alkali). It relates to the balance of carbon dioxide in water and is a function of pH.

Typically, hard water is alkaline, while soft water is more acidic.

If alkalinity is much less than total hardness it may signify elevated levels of chloride, nitrate or sulfate.

The three primary alkali ions in water that contribute to alkalinity are:

  • Bicarbonate (HCO 3 -)

  • Carbonate (CO 3 2 -)

  • Hydroxide (OH -)

Total Alkalinity

Total alkalinity is a measure in parts per million of all the alkali (all carbonate, bicarbonate and hydroxide ions) present in a sample. Therefore, total alkalinity is a measurement of water’s ability to resist changes in pH.

Total alkalinity is determined by titration to a pH of 4.9, 4.6, 4.5, or 4.3, depending on the amount of carbon dioxide present.

Total alkalinity is affected by environmental factors; rain, acidic sanitizers, addition of fill water and other product applications can all change the alkalinity over time. Most alkalinity in surface water comes from calcium carbonate, CaCO3, being leached from rocks and soil

Why Conduct an Alkalinity Test?

Alkalinity is an important factor in a wide variety of applications, from drinking water and beverages to boiler/cooling water and wastewater treatment, as well as many types of manufacturing and chemical production.

  • High alkalinity can mitigate heavy metals toxicity by using available bicarbonates and carbonates to remove metals from solutions.

  • In natural environments, low alkalinity makes streams, rivers or lakes vulnerable to acidic pollutants which can drop the pH of water to levels harmful for amphibians, fish or zooplankton.

  • Alkalinity is needed to buffer or stabilize pH in order to facilitate anaerobic digestion phase of the wastewater treatment.

· When consumed, highly alkaline water has an objectionable "carbonated drink" taste and can be harmful to human health.

· Water that is too alkaline has a bitter taste. It can cause deposits that encrust pipes and appliances. Highly acidic water may corrode metals or even dissolve them.


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