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What Is Demineralized Water?

Demineralized water is water without its mineral and salt ions. Demineralised water is also known as demi water or deionised water.

Demineralized Water
Demineralized Water

Introduction to Demineralized Water (or Deionized Water)

Demineralized water that has had the non-water related ions removed. Demineralization of water is the removal of essentially all inorganic salts by ion exchange. In this process, strong acid cation resin in the hydrogen form converts dissolved salts into their corresponding acids, and strong base anion resin in the hydroxide form removes these acids. Demineralization produces water similar in quality to distillation at a lower cost for most fresh waters.

Tap water typically contains ions from the compost such as sodium, calcium, and magnesium, as well as metal ions from the pipes such as iron and copper. It is deionized by passing it through an ion exchange column, which is an equipment containing a resin that selectively binds with ions in water. Ionized water enters the system and deionized water is the result of the process. Organic contaminants, viruses, and bacteria are not removed during this process.

What Is Demineralized Water Used For?

Demineralized water or deionized water is mostly used in food processing applications, where is combined with membrane filtration, so organic material, bacteria, viruses, can be eliminated beforehand.

Demineralized water is also required in pharmaceutical manufacturing and cosmetics industries that require high levels of water purity.

Demineralised Water Applications and Most Common Uses

Demineralized most common applications include:

  • Pharmaceutical manufacturing.

  • Laboratory applications and testing.

  • Automotive industry.

  • Boiler feed.

  • Semiconductors.

  • Cosmetic industry.

  • Food industry.

How To Make Demineralized Water?

The most common methods for making demineralized water are distillation, reverse osmosis, and deionization processes.

Distillation and deionization are typically only used in industrial or commercial settings, while reverse osmosis is used in commercial and residential environments.

Reverse Osmosis (RO) and Continuous Electrodeionization (CEDI)

Continuous electrodeionization (CEDI) process
Continuous Electrodeionization (CEDI) Process

Due to a deionization process, the water is completely free (or almost) of dissolved minerals such as:

  • Sodium

  • Calcium

  • Iron

  • Copper

  • Chloride / Sulfate

Thanks to this process demineralized water is one of the most pure forms of water.

Advantages and Limitations of Demineralized Water

Demineralizers can produce high-purity water for nearly every use. Demineralized water is widely used for high pressure boiler feedwater and for many process waters. The quality of water produced is comparable to distilled water, usually at a fraction of the cost.

Demineralizers come in a wide variety of sizes. Systems range from laboratory columns that produce only a few gallons per hour to systems that produce thousands of gallons per minute.

Like other ion exchange systems, demineralizers require filtered water in order to function efficiently. Resin foulants and degrading agents, such as iron and chlorine, should be avoided or removed prior to demineralization. Anion resins are very susceptible to fouling and attack from the organic materials present in many surface water supplies.

Some forms of silica, known as colloidal, or non-reactive, are not removed by a demineralizer. Hot, alkaline boiler water dissolves the colloidal material, forming simple silicates that are similar to those that enter the boiler in a soluble form. As such, they can form deposits on tube surfaces and volatilize into the steam.


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