Orapi Asia

What Is Hardness of Water and How to Deal With It

what are the effects of using hard water
Water is a fundamental element of life, indispensable for human consumption, sanitation, and industrial processes. Yet, not all water is created equal. As it journeys through the Earth’s crust, minerals and ions, alter its composition, which impacts its quality and usability. One such transformation is the phenomenon known as “water hardness.”
In water chemistry, hardness refers to the concentration of certain minerals, predominantly calcium and magnesium ions, dissolved within the water. While these minerals are essential for human health and even considered beneficial, their excessive presence in water can lead to many challenges, affecting both household and industrial applications.

What Is the Hardness of Water

In scientific terms, water hardness is generally the dissolved calcium and magnesium concentration in water. But in layperson’s terms, you may notice water hardness when your drinking glasses at home become less than crystal clear or when your hands still feel slimy after washing with soap and water. This is because hard water does not lather when it interacts with soap due to the presence of soluble bicarbonates, chlorides and sulphates of calcium and magnesium.

Measure of Hardness of Water

Hard water arises from the presence of calcium and magnesium compounds, along with various other metal elements. A general framework for classifying water hardness is as follows: water containing 0 to 60 mg/L (milligrams per litre) of calcium carbonate is categorised as soft; water with 61 to 120 mg/L is considered moderately hard; water with 121 to 180 mg/L falls into the hard category; and water exceeding 180 mg/L is classified as very hard.

Water supply systems reliant on groundwater sources encounter concerns regarding water hardness. As water traverses soil and rock, it dissolves trace amounts of naturally occurring minerals, which are then carried into the groundwater supply. Calcium and magnesium readily dissolve in water, and if these minerals are present in the soil surrounding a well, households and establishments may receive hard water.
As the image of the inside of a water-supply pipe shows, extended exposure to hard water can lead to accumulating what is called scale buildup. Analogous to how cholesterol buildup can narrow blood vessels within the human body, water pipes can gradually constrict, resulting in reduced water flow and diminished water pressure.

Alkaline vs Acidic Solutions and Hard Water

the relationship between ph and hydrogen ions concentration

Hard Water and Alkaline Solutions

In a previous article, we mentioned why acidic solutions are more effective at removing mineral stains. Let us now explain why alkaline solutions (or soaps) are comparatively ineffective at removing hard water stains. 
Soap molecules have a polar structure, with a hydrophilic (water-attracting) “head” and a hydrophobic (water-repelling) “tail.” When soap is added to water, the hydrophobic tails of the soap molecules aggregate together, while the hydrophilic heads remain attracted to the surrounding water molecules. This arrangement forms micelles, which can trap and suspend dirt, oils, and other impurities, allowing them to be rinsed away.
However, calcium and magnesium ions interfere with the formation of micelles and the lathering process and lead to the formation of soap scum. Soap scum forms from calcium and magnesium ions, which are divalent cations. These ions react with the hydroxide ions (OH-) in alkaline solutions and form insoluble compounds. This soap scum reduces the effectiveness of the soap, making it less able to create a stable lather and making it harder to dissolve dirt and oils. In addition to inhibiting lather formation, soap scum can lead to buildup on surfaces, such as bathtubs, sinks, and dishes, and can leave a residue on your skin and hair. 

Hard Water and Acidic Solutions

A neutralisation reaction occurs when hard water, containing calcium and magnesium ions, interacts with an acidic solution. The acidic solution donates hydrogen ions (H+) to the water, reducing the concentration of hydroxide ions (OH-) that are responsible for forming insoluble compounds with the calcium and magnesium ions. As a result, acidic solutions do not provide the hydroxide ions that readily react with these ions to form insoluble compounds. Instead, the hydrogen ions from the acid may combine with the carbonate ions (CO3^2-) that can be present in hard water, forming carbon dioxide gas (CO2) and water (H2O), reducing the potential for unwanted precipitate formation.
Because acidic solutions help reduce the concentration of hydroxide ions and minimise the formation of insoluble compounds, they can enhance the cleaning effectiveness in hard water. Acidic solutions can break down minerals and remove stains by dissolving or chelating (binding) with the metal ions in hard water, facilitating their removal from surfaces. 

Types of Hardness of Water

Water hardness that is caused by calcium bicarbonate is known as temporary

Temporary Hardness in Water

The presence of magnesium and calcium carbonates in water makes it temporarily hard. In this case, the hardness in water can be removed by the following methods.

How to Remove Temporary Hardness of Water

In both methods mentioned below, the goal is to convert the soluble bicarbonate compounds into insoluble carbonate compounds, which can then be physically separated from the water through filtration. By removing these insoluble compounds, the hardness of the water is reduced, resulting in water that is less likely to cause scale buildup in pipes and appliances. It’s important to note that these methods only temporarily remove water hardness, as the removed compounds can precipitate again over time.

Boiling Method
When hard water is boiled, the soluble bicarbonate compounds present in the water (such as calcium bicarbonate and magnesium bicarbonate) undergo a chemical change. Boiling causes these bicarbonates to decompose into their corresponding insoluble carbonates, which then form solid particles. These solid particles are removed from the water through a process called filtration. The chemical reactions for calcium bicarbonate (Ca(HCO3)2) and magnesium bicarbonate (Mg(HCO3)2) are as follows:
a. Calcium Bicarbonate Decomposition:
Ca(HCO3)2 → ΔCaCO3↓ + H2O + CO2
b. Magnesium Bicarbonate Decomposition:
Mg(HCO3)2 → ΔMgCO3↓ + H2O + CO2
In both reactions, the bicarbonate ions (HCO3⁻) break down into insoluble carbonate compounds (CaCO3 or MgCO3), water (H2O), and carbon dioxide (CO2). The resulting solid carbonates can be removed from the water through filtration, leaving the water with reduced hardness.
Clark's Method
Clark’s method involves using calcium hydroxide (Ca(OH)2), also known as lime water or Clark’s reagent. When calcium hydroxide is added to hard water, it reacts with the calcium bicarbonate present in the water, forming insoluble calcium carbonate (CaCO3) solid particles. This process reduces the concentration of calcium bicarbonate and thus reduces the overall water hardness. The reaction can be represented as follows:
Ca(OH)2 + Ca(HCO3)2 → 2CaCO3↓ + 2H2O
In this reaction, calcium hydroxide reacts with calcium bicarbonate to produce insoluble calcium carbonate and water.

Permanent Hardness in Water

When water contains the soluble magnesium and calcium salts in the chloride and sulphate forms, it is termed permanent hardness. This type of hardness cannot be removed through boiling.

How to Remove Permanent Hardness of Water

In all three methods mentioned below, the goal is to remove the calcium and magnesium ions that contribute to water hardness. These methods rely on chemical reactions or adsorption processes to reduce the concentration of these ions, resulting in softened water that is less likely to cause scale buildup and other issues associated with hard water.

Gan's Permutit Method
In this method, sodium aluminium ortho silicate, commonly known as permutit or zeolite, removes permanent hardness from water. Permutit is a type of ion exchange material that can exchange sodium ions (Na⁺) for calcium ions (Ca²⁺) and magnesium ions (Mg²⁺) in the water. The chemical reaction can be represented as follows:
Na2Al2Si2O8.KH2O + Ca²⁺ → 2Na⁺ + CaAl2Si2O8.xH2O
In this reaction, permutit exchanges sodium ions for calcium ions, removing calcium ions from the water. This process helps reduce the overall hardness of the water.
Calgon's Process

In the Calgon process, sodium-hexa-meta-phosphate (NaPO3)6, commonly known as Calgon, is used. Calgon works by adsorbing (adhering to the surface) calcium ions (Ca²⁺) and magnesium ions (Mg²⁺) present in the water. This reduces the concentration of these ions and thus reduces water hardness. The process involves the adsorption of Ca²⁺ and Mg²⁺ ions by the Calgon particles.

Ion Exchange Resin Method

In this method, ion exchange resins remove permanent hardness from water. Ion exchange resins are specially designed materials with functional groups that can reversibly exchange ions. In water softening, cation exchange resins remove calcium and magnesium ions. In contrast, anion exchange resins are used to remove sulphate ions.

For cation exchange:

Ca²⁺/Mg²⁺ + 2RCOOH → (RCOO)2Ca/Mg + 2H⁺

For anion exchange:

RNH2OH + Cl⁻ → RNH2Cl + OH⁻

H⁺ + OH⁻ → H2O

In the cation exchange, the resin exchanges hydrogen ions (H⁺) for calcium and magnesium ions, removing these ions from the water. In the anion exchange, the resin removes chloride ions (Cl⁻) and hydroxide ions (OH⁻) to maintain electroneutrality.

Problems Caused by Hard Water

disadvantages of hard water

Laundry Issues

Hard water doesn’t lather well with soap, making it less effective for laundry purposes. This can lead to poor cleaning of clothes.


Hard water contains high levels of minerals like calcium and magnesium, which can deposit onto fabric fibres during washing. This mineral buildup can make clothes feel stiff and rough. Many like to use fabric softeners to combat the stiffness that results from hard water usage. 

Dulling of Colors

The minerals in hard water can also react with laundry detergents, forming a residue that dulls the colours of clothes over time.

Soap Scum

Hard water can prevent detergents from lathering properly, leading to soap scum buildup on clothes. This can make fabrics appear dingy and feel less clean.

Reduced Cleaning Effectiveness

Hard water can reduce the effectiveness of laundry detergents by interfering with their ability to remove dirt and stains from clothes.

Skin Irritation

Hard water can strain the skin and hair, leading to dryness and irritation for those who use it for bathing.

Increased Water Appliance Workload

Appliances like water heaters, dishwashers, and washing machines have to work harder when using hard water, potentially increasing water bills and energy consumption.

Spots on Clothes and Linens

Hard water can cause mineral deposits to form on clothes and linens, leaving behind unsightly spots.

Formation of Scales

Boiler Efficiency Reduction

Hard water can lead to the deposition of salts in boilers, reducing their efficiency over time.

Equipment Efficiency Reduction

Mineral deposits, scale or limescale, can accumulate on equipment surfaces and pipelines. This reduces the efficiency of heat exchangers, pumps, and other components, increasing energy consumption.

Toilet Bowl Deposits

Hard water can lead to mineral deposits accumulating in toilet bowls, resulting in the formation of limescale.

Steel, Copper, & PVC Pipes

As steel pipes near the end of their lifespan, calcium and magnesium buildup, known as lime scale, will increasingly obstruct them. This problem isn’t limited to steel pipes alone; PVC and copper pipes can also become blocked over time due to mineral deposits. Signs of this issue include reduced water pressure and the presence of particles in your faucet or shower water. Moreover, rising pipe pressure can lead to cracks forming, causing water to divert to other areas of your home before reaching the desired sink or fixture. 


Soap Scum

The reaction between hard water and soap can lead to the formation of scum, wasting soap and making cleaning less effective.

Excessive Fuel Consumption

Industries that use hard water for processes may need more fuel to sustain extended and intensified machine operation due to the increased workload caused by hard water.

Common Signs of Hard Water

  • Linens and garments lose their lustre and exhibit a coarse texture.
  • Unattractive blemishes on white ceramic surfaces accompanied by mineral deposits on faucets.
  • Reduced shower water pressure resulting from obstructed pipelines.
  • Formation of chalky, white marks or patches on dishware.
  • Visible streaks and marks emerge within the shower area.

How to Treat Hard Water

water softener tank inside a building

Water Softener

A Water Softener is the main way to deal with hard water. This system purifies water by removing hard minerals. Water passes through a resin bed that captures calcium and magnesium, replacing them with sodium ions through ion exchange.
A water softener requires salt for proper function. A separate tank, the brine tank, holds water softener salt and is crucial for regeneration. Sodium-enriched water from the brine tank cleans the resin bed during regeneration, removing accumulated minerals from the system.

Water Conditioner

Water conditioners utilise template-assisted crystallisation (TAC) media to crystallise the minerals responsible for water hardness. This process effectively inhibits the accumulation of scale within pipes and appliances. Unlike water softeners that employ ion exchange resin to extract these minerals from water, water conditioners bring about physical alterations to the minerals, thereby impeding their ability to cause scaling issues.

Conclusion: What Is Water Hardness

In conclusion, understanding the intricacies of water hardness is crucial for optimising the use of this vital resource. While minerals like calcium and magnesium are essential for health, their excessive presence in water can lead to various challenges, affecting household and industrial applications. This article has delved into the concept of water hardness, its effects on cleaning efficiency, and methods for its removal. From temporary to permanent hardness, the implications of hard water encompass laundry woes, skin irritation, equipment inefficiencies, and more. By comprehending the nuances of water hardness, we can make informed decisions to ensure efficient, sustainable, and effective utilisation of water resources in various contexts.

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