The key difference between temporary and permanent hardness of water is that temporary hardness of water can be removed by boiling the water, whereas permanent hardness cannot be removed by boiling.
We can define water hardness as the measurement of the concentration of total divalent ions present in water. Examples of some divalent ions present in water are calcium ion, magnesium ions, and Fe2+ ion. However, calcium and magnesium are the most common sources of water hardness. The unit for hardness is ppm per CaCO3 equivalents. There are two types of water hardness: temporary and permanent hardness of the water. Temporary hardness occurs due to the presence of calcium hydrogencarbonate and magnesium hydrogencarbonate while permanent hardness occurs due to sulfates and chlorides of magnesium and calcium.
CONTENTS
1. Overview and Key Difference
2. What is Temporary Hardness of Water
3. What is Permanent Hardness of Water
4. Side by Side Comparison – Temporary vs Permanent Hardness of Water in Tabular Form
5. Summary
What is Temporary Hardness of Water?
Temporary hardness occurs due to the presence of calcium hydrogencarbonate (Ca (HCO3)2) and magnesium hydrogencarbonate (Mg (HCO3)2). Both species decompose when heated and CaCO3 or MgCO3 precipitation occurs. Therefore, temporary hardness can be removed by boiling water.
When minerals such as calcium bicarbonate and magnesium bicarbonate dissolve in water, it yields calcium and magnesium cations (Ca2+ and Mg2+) along with carbonate and bicarbonate anions. These metal ions present in the water sample cause the hardness of the water. Other than boiling water, we can remove the temporary hardness of water through the addition of lime (lime is calcium hydroxide). This addition process is known as lime softening.
What is Permanent Hardness of Water?
Permanent hardness is due to sulfates and chlorides of magnesium and calcium. In other words, permanent water hardness occurs when water contains calcium sulfate or calcium chloride and/or magnesium sulfate or magnesium chloride. Therefore, we can say that the permanent hardness is equal to the sum of the permanent calcium hardness and permanent magnesium hardness.
Figure 01: Calcification due to Hard Water
These minerals do not precipitate when heated. Therefore, permanent hardness cannot be removed simply by boiling. We can remove permanent water hardness either using a water softener or using an ion-exchange column.
What is the Difference Between Temporary and Permanent Hardness of Water?
Temporary hardness occurs due to the presence of calcium hydrogen-carbonate (Ca (HCO3)2) and magnesium hydrogen-carbonate (Mg (HCO3)2). Permanent hardness is due to sulfates and chlorides of magnesium and calcium. The key difference between temporary and permanent hardness of water is that temporary hardness of water can be removed by boiling the water, whereas permanent hardness cannot be removed by boiling. Therefore, we need to use another method to remove permanent hardness from water, such as the addition of using a water softener or using an ion-exchange column.
The following infographic summarizes the differences between temporary and permanent hardness of water in tabular form.
Summary – Temporary vs Permanent Hardness of Water
Hard water is water that has a high mineral content. There are two types as temporary and permanent hardness of the water. Hard water cause precipitation of soap from soap water. It forms deposits that clog plumbing. Therefore, it is important to know the removal processes of water hardness. The key difference between temporary and permanent hardness of water is that temporary hardness of water can be removed by boiling the water, whereas permanent hardness cannot be removed by boiling.
Reference:
1. Arthur, Daniel. “Temporary And Permanent Hardness of Water.” Water Treatment Basics, 25 June 2019, Available here.
Image Courtesy:
1. “Hard Water Calcification” By Bbypnda – Own work (CC BY-SA 3.0) via Commons Wikimedia