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What is the Difference Between De-Mineralized Water and Purified Water?

Water is one of the most essential resources on earth. It has multiple uses across the globe, from consumption to agriculture, from manufacturing to electronics. Water is a vital element in the modern manufacturing industries that utilize water as an ingredient, for cleaning purposes, for diluting other strong liquids, as a stabilizer, and also used to transport things around. Modern industries have found innovative and judicious uses of water that were never imagined before. With a rise in demand for products and consumer goods, there was a simultaneous increase in the pressure on usable water sources.

Water is a critical component in the Pharmaceutical manufacturing industry. It is used as raw material, ingredient, and solvent in the processing, formulation, and manufacture of pharmaceutical products and medical devices. However, the quality of water used for each of these purposes is different. For example, water used as a raw material has more stringent purity regulations as compared to water used for cleaning the factory/plant premises. Still, the quality of water for pharmaceutical use needs to comply with various international purity standards. 

Different grades of pure water are used to produce pharmaceutical products and medical devices. Manufacturers need to ensure the water treatment systems used to produce purified water are designed as per the required quality standards. A number of water purification processes are used to produce water that is up to the mark for use in pharmaceutical industries.

Demineralization is essentially removing all the minerals that can be found in natural water. This process is usually done when the water will be used for chemical processes and the minerals present may interfere with the other chemicals. All the mineral and salt ions that are responsible for the hardness of water are removed from the raw water, such as Calcium, Magnesium, Sodium, Chloride, Sulphate, Nitrate and bicarbonate.

In the De-Mineralization process, Ion exchange resins play a main role.

The following ions are widely found in raw waters:



Calcium (Ca2+)

Chloride (Cl-)

Magnesium (Mg2+)

Bicarbonate (HCO3-)

Sodium (Na+)

Nitrate (NO3-)

Potassium (K+)

Carbonate (CO32-)

Ion Exchange Resins
  • There are two basic types of resin – cation-exchange and anion-exchange resins. Cation exchange resins will release Hydrogen (H+) ions or other positively charged ions in exchange for impurity cations present in the water. Anion exchange resins will release hydroxyl (OH-) ions or other negatively charged ions in exchange for impurity anions present in the water.
  • The application of ion-exchange to water treatment and purification. There are three ways in which ion-exchange technology can be used in water treatment and purification:

  1. Cation-exchange resins alone can be employed to soften water by base exchange;
  2. Anion-exchange resins alone can be used for organic scavenging or nitrate removal;
  3. Combinations of cation-exchange and anion-exchange resins can be used to remove virtually all the ionic impurities present in the feed water, a process known as deionization. Water deionizers purification process results in water of exceptionally high quality.

  • This water is also called soft water because all the hardness is removed by the de-mineralization process.
  • Generally, soft water is used in boilers to produce the stem because it does not create the problem of scaling in the boilers. Soft water is also used to feed purified water plant.
  • All cosmetic and beauty products have to be made with demineralized water for this reason. With the demineralization process, the water is “softened” replacing the undesired minerals with different salts(NaCl).

Let’s take a look at some of the most commonly used grades of water and the processes used to produce them:

1. Demineralized Water
  • Demineralization is the process of removal of certain minerals from feed water. In its natural state, water contains innumerable impurities and minerals that make it unfit for use with machinery. This impure water is called hard water. Hard water can be especially harmful to the internal parts of machines and systems employed in the pure water plant. It can severely corrode the metal parts and cause the rapid rusting of the parts. Hence, removing minerals from hard water is a very essential step in any purified water system. All minerals responsible for the hardness of water are eliminated and demineralized water is produced.
  • A process called Ion Exchange is used to remove the dissolved minerals and salts. The anion exchange resin removes minerals with a positive charge and a cation exchange resin removes minerals and salts with a negative charge. This process eliminates the impurities responsible for the hardness of water and makes it soft. Soft water is generally used in boilers to make steam. It is also used as feed water in other purification plants.

2. Purified Water
  • Purified water is highly purified water as compared to demineralized water. It is produced bypassing demineralized water through another purification process for further filtration. Methods such as Reverse Osmosis or UV light purification are used to further purify water. When soft water passes through the fine filters in an RO membrane, the impurities are left behind in the filter and pure water comes out the other side. Additionally, the fine filters are capable of removing microbial contamination from water.
  • Purified water is used in pharmaceutical manufacturing units to produce water for injection or WFI, and high purity water is used in the formulation of parenteral (injectable) drugs. Multi-column distillations are used to produce purified water. A distillation plant converts the feedwater into steam and then a condensation process is used to convert the steam into purified water.
  • Purified water needs to pass a number of purity tests ranging from pH, conductivity, hardness, heavy metal, and microbial limit tests. Manufacturers need to ensure that the purified water used for the production of pharmaceutical products in their plant is compliant with regulations set in place by USFDA, EU, and ISI.
  • Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use and produced using DM water. To prepare the purified water, DM water is passed through a Reverse Osmosis membrane and ultraviolet light. Reverse Osmosis removes the soluble impurities from the water by passing water through its membrane having a pore size of 0.0003μ.
  • Ultraviolet removes microbes from the water making it free from microbial contamination.
  • Purified water is also used in the pharmaceutical industry. The water of this grade is widely used as raw material, ingredient, and solvent in the processing, formulation, and manufacture of pharmaceutical products, active pharmaceutical ingredients (APIs)and intermediates, compendial articles, and analytical reagents.
  • Purified water is also used to produce water for injection. It is distilled in a multi-column distillation plant and collected by the condensation process.

Both DM water and purified water have their own specifications to be passed their quality. DM water should pass the hardness and pH test only while purified water has various parameters like description, conductivity, pH, heavy metal, hardness, nitrate, sulfate, iron, residue on evaporation, microbial limit test etc.

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