Hardness of Water: Temporary and Permanent Hardness

Hardness of Water is caused due to the presence of soluble bicarbonates, chlorides, and sulfates of calcium and magnesium. Hard water is water that does not lather when soap is added. There might be some small health benefits in drinking hard water. It can present severe problems in factories where water hardness is monitored to prevent expensive breakdowns in boilers, cooling towers, and other water-handling equipment.

In this article, we will learn, what is hardness of water, the types of hardness, how to remove it along with the disadvantages and harmful effects of the hardness of water.

What is Hardness of Water?

Hardness of water refers to the concentration of minerals, primarily calcium and magnesium ions, dissolved in water. These minerals can make water “hard,” affecting its ability to lather with soap and causing issues like scale buildup in pipes and appliances. The hardness level is commonly measured in terms of milligrams per liter (mg/L) or parts per million (ppm). Understanding water hardness is crucial for various applications, including household activities, industrial processes, and water treatment.

Classification of Water

The classification of water is divided in two types:

• Soft Water
• Hard Water

Soft Water

When soap is added, it lathers. Rainwater is a type of soft water. You can use this water for cleaning and laundry in the home.

Hard Water

The water is called hard water because of the calcium and magnesium salts. Hard water causes a precipitate to form instead of lathering with soap.

What Is Hard Water?

Hard water contains a lot of minerals. It is created when water breaks through the calcium and magnesium carbonate deposits in chalk and limestone layers. It is inappropriate for laundry because it does not produce a lather when soap is added.

Too hard water can damage boilers because it causes salt to build up and lowers the boiler’s performance. Although hard water is safe to drink, consuming it frequently can cause several problems, including:

• Skin stretches
• Water appliances have to work harder, which raises the cost of water.
• Spots show up on linens and clothing.

Hardness of Water Formula

The hardness of water is typically quantified using the following formula:

Hardness (mg/L or ppm) = (Equivalent Weight of CaCO₃ × Volume of EDTA solution (mL) × Normality of EDTA solution) / Volume of Water Sample (L)

In this formula:

• Equivalent Weight of CaCO3Equivalent Weight of CaCO_3​ is the equivalent weight of calcium carbonate,
• Volume of EDTA solutionVolume of EDTA solution is the volume of the ethylenediaminetetraacetic acid (EDTA) solution used in the titration,
• Normality of EDTA solutionNormality of EDTA solution is the normality of the EDTA solution, and
• Volume of Water SampleVolume of Water Sample is the volume of the water sample being tested.

Types of Hardness of Water

There are two categories of hardness of water:

• Temporary Hardness 
• Permanent Hardness

Temporary Hardness of Water

Water becomes instantly hard due to the carbonates of calcium and magnesium present. In this situation, boiling the water will remove the hardness.

When water is boiled, the soluble salts of magnesium(HCO3)2 are changed into the insoluble magnesium(OH)2, this forms precipitates and is eliminated. We obtain soft water as a result of filtration.

Permanent Hardness of Water

Since boiling cannot eliminate the soluble compounds of calcium and magnesium from water, the presence of these salts in the form of chlorides and sulfides is referred to as persistent hardness.

By using washing soda to treat the water, we may get rid of this hardness. When washing soda combined with calcium magnesium sulfide and chloride salts, insoluble carbonates are created, turning hard water into soft water.

Difference Between Temporary and Permanent Hardness of Water

The difference between temporary and permanent hardness of water can be understood from the table below:

Temporary Hardness vs Permanent Hardness
Characteristic	Temporary Hardness	Permanent Hardness
Origin	Caused by bicarbonate ions (HCO₃⁻) in water.	Caused by chlorides, sulfates, or nitrates of calcium and magnesium in water.
Removal by Boiling	Removed by boiling water.	Not removed by boiling water; remains after boiling.
Formation of Scale	Causes scale formation when water is heated.	Causes scale formation both when heated and in normal conditions.
Effect on Soap Lathering	Reduces soap lathering ability.	Does not significantly affect soap lathering.
Chemical Precipitation	Can be precipitated by adding lime Ca(OH)2	Cannot be easily precipitated by common methods; often requires water softening techniques.
Hardness Salts	Mainly bicarbonates of calcium and magnesium.	Mainly sulfates, chlorides, and nitrates of calcium and magnesium.
Health Impact	Generally not harmful to health.	Not harmful but can be problematic for industrial processes and can contribute to scale buildup.

Methods to Remove Temporary Hardness of Water

The methods to remove temporary hardness of water are:

• Clarks Method
• Boiling Method

By Clarks Method

The reagent used by Clark is calcium hydroxide. By changing bicarbonates into carbonate, it takes off the hardness of the water.

Reaction: Ca(OH)2 + Ca(HCO3)2 → 2CaCO3↓ + 2H2O

By Boiling

Filter is used to eliminate insoluble carbonates that are created from soluble bicarbonates.

Reactions: Ca(HCO3)2 → ΔCalo3↓ + H2O + CO2

⇒ Mg(HCO3)2 → ΔMgCO3↓ + H2O + CO2

Methods to Remove Permanent Hardness of Water

The methods to remove permanent hardness of water are:

• Calgon’s Process
• Ion Exchange Resin Method
• Gan’s Permutit Method

Calgon’s Process

Calgon, also known as sodium-hexa-meta-phosphate (NaPO3)6, is used in this procedure. The process of Ca++ and Mg++ ions adhering to water molecules eliminates its hardness.

Ion Exchange Resin Method

Resins are used in this procedure to permanently eliminate the hardness of the water. Cl– is used to exchange Ca++/Mg++ ions, while anion exchange resin (RNH2OH) is used to exchange SO4-2 ions. In the procedure, demineralized water is produced.

2RCOOH + Ca²⁺ → (RCOO)2Ca + 2H⁺

RNH₂OH + Cl^– → RNH₂Cl + OH–

 H⁺ + OH^– → H₂O

Gan’s Permutit Method

This technique uses sodium aluminum ortho silicate, sometimes referred to as zeolite or permutite, to take out the water’s persistent hardness.

Reaction: Na₂Al₂Si₂O₈.KH₂O + Ca²⁺→ 2Na⁺ + CaAl₂Si₂O₈.xH₂O

Harmful Effects of Hard Water

The harmful effects of hard water are:

• Clothes and linens have a harsh, dull appearance.
• White porcelain with ugly spots and faucets with scale build-up
• Clogged pipes causing low shower water pressure.
• Dishes have stains or residues that are chalky or white.
• Stress starts to show in the shower.

Disadvantages of Hard Water

The disadvantages of Hard water are:

• Dishes, hair, and laundry lose the sudsy fight.
• Pipes cloggs, their durability decreases and machines requires service often.
• Water spots and mineral ghosts haunt your bathroom. The sparkling surfaces of bathroom vanishes leaving water spots
• Clothes comfort, colors disappers and fabric stiffens. 
• Hard water removes the moisture from skin which leads to itchiness and irritation.
• Using hard water machines get damaged and the cost and time for repairs and replacement increases.

Hardness of Water – Conclusion

• Hardness of Water is due to dissolved salts of calcium and magnesium
• There are two types of Hardness, namely, Temporary and Permanent Hardness of Water.
• Temporary Hardness can be removed by Clark’s Method and Boiling
• Permanent Hardness of water can be removed by Calgon’s Method, Ion Exachange Method and Gan Permutit Method
• Hardness of Water is measured in mg/L or ppm
• There are several disadvantages of Hardness of Water such as no formation of lather, fabric stiffness, water spots, removal of moisture from skin etc.

Hardness of Water – Frequently Asked Questions

What is the reason of Hardness water?

The main reason of Hardness of water is presence of soluble salts of calcium and magnesium salts in water.

What are the types of Hardness of Water?

There are two types of harness of water:

• Temporary Hardness of Water
• Permanent Hardness of Water

What are some Harmful Effects of Hard Water?

Some harmful effects of hard water are:

• The dull appearance of clothes
• Clogged pipes causing low shower water pressure.

In which unit do we measure water hardness?

Grains per gallon (gpg) or parts per million (ppm) are units of measurement for water hardness.

Define Hardness of Water.

Water hardness is the amount of dissolved minerals, mainly calcium and magnesium, in water. It affects soap lathering and can lead to scale buildup in pipes. Measurement is typically in milligrams per liter (mg/L) or parts per million (ppm).

How to Remove Permanent Hardness of Water?

To remove permanent hardness of water, water softening methods such as ion exchange, lime-soda treatment, or reverse osmosis can be employed. These techniques help replace or remove the calcium and magnesium ions responsible for permanent hardness, resulting in softened water.