Water Hardness can be either Temporary or Permanent. These forms of hardness are discussed below.
Temporary Hardness results when calcium or magnesium are paired with carbonate and bicarbonate in the water. Temporary Hardness can be reduced by boiling treatment and by treatment through lime softening.
Permanent Hardness results when calcium or magnesium are paired with anions such as chloride and sulfate that cannot be driven off by boiling the water. Enhanced softening processes are required to reduce permanent hardness in water. Distillation, deionization, and reverse osmosis (RO) processes are examples of enhanced softening processes.
Total Hardness is the sum of Temporary Hardness and Permanent Hardness in the water.
2.3 Alkalinity
Alkalinity is a measure of the "buffering" capacity of a solution and its ability to neutralize strong acid and resist pH change. Alkalinity is defined as the amount of strong acid required to lower the pH of a sample of the water to a specified pH (typically 4.3 to 4.5). Alkalinity is generally due to the concentration of carbonate (CO3), bicarbonate (HCO3), and hydroxyl (OH-) ions in water. Higher alkalinity water requires more acid to change the pH.
Like hardness, alkalinity tends to vary on a regional basis. The map below illustrates how alkalinity varies across the United States (Omernik & Powers, 1983). As indicated by the map, much of the U.S. has relatively high alkalinity in surface waters. Of the regions with reduced alkalinity, many are mountainous or are regions without carbonate rock near surface. Carbonate rock and soils impart alkalinity to water
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