Difference Between Alkalinity And Hardness

Alkalinity and hardness are terms used to describe the levels of certain ions in water. Alkalinity is a measure of the total amount of alkaline substances like carbonates, hydroxides, bicarbonates, and other compounds found in water. Hardness is a measure of calcium and magnesium content in water. Alkalinity helps to prevent water from becoming overly acidic and is important for aquatic life. Hardness, on the other hand, helps protect against scale and provides an aesthetic taste in water. Generally, hard water is preferred over soft water because of its ability to rinse the soap off more effectively, though this will depend mainly on the individual’s preferences.

What Is Alkalinity?

What Is Alkalinity

Alkalinity measures the buffering capacity of an aqueous solution, meaning its ability to resist changes in pH when additional acid or base is added. Alkalinity is typically measured in milligrams per liter (mg/L) of calcium carbonate (CaCO3). The alkalinity of water is primarily composed of carbonates, bicarbonates, and hydroxides.

What Is Hardness?

What Is Hardness
Hardness of water

The hardness of water measures the concentration of certain metallic elements, such as magnesium and calcium, found in it. These metals can react with soaps, making them less effective and leaving behind scum in the laundry. Hardness is usually measured in milligrams per liter (mg/L) as calcium carbonate (CaCO3). Hardness has two types:

  • Temporary Hardness: This is the hardness caused by the dissolved bicarbonates of calcium and magnesium. B boiling can remove it from water, leading to calcium carbonate precipitation.
  • Permanent Hardness: This is the hardness caused by chlorides and sulfates of calcium and magnesium. This hardness is not removed by boiling and can only be reduced using a water softener.

What Are The Similarities Between Alkalinity And Hardness?

What Are The Similarities Between Alkalinity And Hardness
Similarities Between Alkalinity And Hardness
  • Both Alkalinity and Hardness are measures of water quality.
  • Hardness is a measure of the number of minerals in the water, while alkalinity is a measure of the ability of water to neutralize acids.
  • Alkalinity and hardness both affect the taste of water.

What Is The Difference Between Alkalinity And Hardness?

  • Causative species: Alkalinity is caused by the presence of carbonate species. The hardness of water is caused by divalent ions such as calcium, magnesium, or iron ions.
  • Determination: Alkalinity is determined by acid-base titrations.in contrast, you can determine the hardness by EDTA titration.
  • Reactions titration: Carbonate species that cause alkalinity can react with strong acids in the presence of phenolphthalein and methyl orange indicators to change color when all carbonate ions are consumed. This titration is generally carried out to measure alkalinity. On the other hand, hardness in water can be measured by EDTA titration, which involves the reaction of calcium and magnesium ions with EDTA to form a complex that changes color when all calcium and magnesium are consumed.

Natural Factors Influencing Alkalinity

  • Geology: Alkalinity is primarily affected by the geology of a region. Areas with abundant limestone and other carbonate rocks have higher alkalinity than those without.
  • Weather: Temperature and precipitation can also affect alkalinity levels in the water, typically increasing colder temperatures due to an increased influx of natural materials from rivers and streams.
  • Seasonal weather: Spring, snow, and rain can increase the alkalinity.
    Seasonal weather
    Seasonal weather

Human Factors Influencing Alkalinity

  • Acid Mining Waste: Acid mine drainage results from the oxidation of iron sulfide (pyrite), which releases acidity into nearby water bodies, which can significantly affect the water’s alkalinity.
    Acid Mining Waste
    Acid Mining Waste
  • Agricultural Runoff: Fertilizers and other agricultural chemicals used in crop production can contain high levels of nitrates and phosphates, which can cause significant increases in alkalinity if they are present in the water.
    Agricultural Runoff
    Agricultural Runoff
  • Urbanization: Urban development, such as construction and pavement, can lead to increased levels of sediment, organic matter, and other materials in the water, which can increase alkalinity.


Does boiling reduce the hardness of water?

No, boiling does not reduce the hardness of the water.

What is the purpose of raising alkalinity in water?

Alkalinity is essential in water to help buffer against pH changes. It works with the other components of water chemistry to maintain a neutral balance and provide stability. An alkalinity level between 6-12 dKH (degrees of Carbonate Hardness) is recommended in freshwater aquariums. Alkalinity helps protect fish from rapid pH swings, which can harm their health and well-being.

How good is water with excess alkalinity?

Water with excess alkalinity is not necessarily good for your health, as it may contain high concentrations of calcium and magnesium, which can lead to hard water. Hard water can form scale on pipes and other equipment, leading to clogging or reduced flow rate. High alkalinity levels in drinking water can also make the taste unpleasant and lead to the staining of porcelain fixtures.

Does alkaline water help heartburn?

Alkaline water may not directly affect heartburn, but its ability to neutralize acidity in the stomach could help reduce symptoms. Alkalinity measures how much alkali, or base, is present in water.

How is alkalinity caused in water?

Alkalinity in water is caused by various natural sources, such as decaying organic matter and chemical compounds like carbonate and bicarbonate ions.

What is carbonate hardness?

What is carbonate hardness
Carbonate hardness

Carbonate hardness, alkalinity, measures the amount of dissolved carbon dioxide in water. It is essential for maintaining a balanced environment in aquariums and ponds because it helps keep pH levels stable by acting as a buffer against changes in acidity or alkalinity. The higher the carbonate hardness (alkalinity), the less likely pH levels will fluctuate, making it essential for fish and plant life.


Alkalinity and hardness both measure the mineral content of water, but they are different in terms of what minerals they measure. Alkalinity measures the amount of bicarbonates and carbonates, while hardness measures the amount of calcium and magnesium. Understanding the difference between alkalinity and hardness is essential for informed water treatment or testing decisions. It is also important to remember that while the two measures are related, they do not always directly correlate. Therefore, it is best to test for both alkalinity and hardness when trying to understand the mineral content of your water.

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