De-ionised Water: Purity Beyond the Tap

Introduction

De-ionised water, also known as demineralised or deionized (DI) water, is a highly purified form of water that has had most or all of its mineral ions removed through a process called deionisation. This specialised water type plays a crucial role in various industrial, scientific, and technological applications where water purity is paramount. Understanding the properties, production methods, and applications of de-ionised water is essential for professionals in fields ranging from laboratory research to industrial manufacturing.

The process of deionisation removes charged ions from water, resulting in a product with very low electrical conductivity and a neutral pH. This unique characteristic sets de-ionised water apart from regular tap water and other purified water types, making it invaluable in settings where even trace amounts of minerals or impurities can interfere with processes or results. For instance, in clinical biochemistry and immunochemistry, the use of de-ionised water is critical for maintaining the accuracy and reliability of test results (Pardue et al., 2018).

De-ionised water finds applications across a wide spectrum of industries and research fields. In laboratories, it serves as a crucial component in the preparation of cell and tissue culture media, molecular biology techniques, and analytical processes such as mass spectrometry and spectrophotometry. Industries such as pharmaceuticals, microelectronics manufacturing, and food production rely on de-ionised water to ensure product quality and process efficiency. Moreover, its low mineral content makes it ideal for use in cooling systems and power generation, where it helps prevent scale buildup and corrosion, thereby extending the lifespan of equipment and reducing maintenance costs (Greenlee et al., 2009).

Here is the main body of the article on de-ionised water:

Understanding De-ionised Water: Definition, Properties, and Applications

What is De-ionised Water?

De-ionised water, also known as demineralised or deionized (DI) water, is a highly purified form of water that has had most or all of its mineral ions removed through a process called deionisation (Greenlee et al., 2009). This specialised water type is produced by removing charged ions from regular water, resulting in a product with very low electrical conductivity and a neutral pH.

The deionisation process typically involves passing water through ion exchange resins that remove positively charged cations (such as calcium, magnesium, and sodium) and negatively charged anions (such as chloride and sulfate). This results in water that is almost completely free of dissolved mineral salts. The purity of de-ionised water can vary depending on the specific process used, but it generally has a conductivity of less than 1 microsiemens/cm, compared to tap water which typically ranges from 50-800 microsiemens/cm (Pardue et al., 2018).

Unlike regular tap water, which contains various dissolved minerals and impurities, de-ionised water is characterised by its exceptional purity. This makes it invaluable in settings where even trace amounts of minerals or contaminants can interfere with processes or results, such as in laboratory experiments, industrial manufacturing, and sensitive equipment operation.

Key Properties of De-ionised Water

De-ionised water possesses several unique properties that distinguish it from other types of water:

1. High Purity Level: The primary characteristic of de-ionised water is its exceptional purity. Most mineral ions and impurities found in regular water are removed, resulting in a product that is nearly pure H2O. The total dissolved solids (TDS) content of de-ionised water is typically less than 1 part per million (ppm), compared to tap water which can range from 50 to over 300 ppm (Greenlee et al., 2009).

2. Low Electrical Conductivity: Due to the absence of charged ions, de-ionised water has very low electrical conductivity. This property is crucial in applications where water's electrical properties could interfere with processes or equipment. The specific conductivity of high-quality de-ionised water can be as low as 0.055 μS/cm at 25°C (Pardue et al., 2018).

3. Neutral pH: Theoretically, pure de-ionised water should have a neutral pH of 7.0. However, in practice, the pH can vary slightly due to dissolved carbon dioxide from the air, which forms weak carbonic acid. The pH of de-ionised water typically ranges from 6.5 to 7.5 (Greenlee et al., 2009).

4. Absence of Dissolved Minerals and Impurities: De-ionised water is free from dissolved minerals like calcium, magnesium, sodium, and potassium, as well as anions such as chloride, sulfate, and bicarbonate. This absence of minerals makes it ideal for applications where mineral deposits could cause problems, such as in cooling systems or laboratory experiments.

5. Reduced Potential for Mineral Buildup and Corrosion: The lack of dissolved minerals in de-ionised water significantly reduces the potential for scale formation and mineral deposits in equipment and pipes. This property is particularly valuable in industrial processes and cooling systems, where mineral buildup can decrease efficiency and increase maintenance costs (Greenlee et al., 2009).

6. High Solvent Capacity: Due to its purity, de-ionised water has an increased capacity to dissolve substances. This makes it an excellent solvent for many laboratory and industrial applications, particularly in the preparation of chemical solutions and reagents (Pardue et al., 2018).

7. Surface Tension: De-ionised water has a higher surface tension compared to regular water due to the absence of dissolved substances. This property can be advantageous in certain applications, such as in the electronics industry for cleaning delicate components (Greenlee et al., 2009).

These unique properties make de-ionised water essential in various fields, from scientific research to industrial manufacturing, where water purity is paramount for achieving accurate results and maintaining equipment efficiency.

The Deionisation Process: Methods and Techniques

Ion Exchange Deionisation

Ion exchange deionisation is the most common method used to produce de-ionised water. This process involves passing water through beds of ion exchange resins, which remove dissolved ions from the water by exchanging them with hydrogen (H+) and hydroxyl (OH-) ions.

The ion exchange process typically involves two types of resins:

1. Cation Exchange Resin: This resin removes positively charged ions (cations) such as calcium (Ca2+), magnesium (Mg2+), and sodium (Na+). The resin beads are initially loaded with hydrogen ions (H+), which are exchanged for the cations in the water.

2. Anion Exchange Resin: This resin removes negatively charged ions (anions) such as chloride (Cl-), sulfate (SO42-), and nitrate (NO3-). The resin beads are initially loaded with hydroxyl ions (OH-), which are exchanged for the anions in the water.

As water passes through these resin beds, the dissolved ions are replaced by H+ and OH- ions, which combine to form water molecules (H2O). This results in highly purified water with very low ionic content.

The efficiency of ion exchange deionisation can be quite high, typically removing 99.9% of dissolved ions from water (Greenlee et al., 2009). However, the process has some limitations:

• Resin Regeneration: Over time, the ion exchange resins become saturated with removed ions and lose their effectiveness. They need to be regenerated periodically using strong acid (for cation resins) or strong base (for anion resins) solutions.

• Organic Contaminants: Ion exchange is not effective at removing uncharged organic molecules or particles.

• Silica Removal: Standard ion exchange resins are not very effective at removing silica, which can be a concern in some high-purity water applications.

Electrodeionisation (EDI)

Electrodeionisation (EDI) is an advanced water purification technology that combines ion exchange resins with ion-selective membranes and an electric field to continuously remove ions from water. This process offers several advantages over traditional ion exchange:

1. Continuous Operation: EDI systems can operate continuously without the need for periodic chemical regeneration of resins.

2. High Purity: EDI can produce water with extremely low ionic content, often achieving resistivity levels above 18 megohm-cm (Pardue et al., 2018).

3. Reduced Chemical Usage: The continuous regeneration of resins through electrolysis eliminates the need for chemical regenerants, making the process more environmentally friendly.

4. Removal of Weakly Ionized Species: EDI is effective at removing weakly ionized species like silica and boron, which are challenging for conventional ion exchange.

Continuous Electrodeionisation (CEDI) systems are a common implementation of EDI technology. In CEDI, water flows through chambers containing ion exchange resins, separated by ion-selective membranes. An electric field is applied across the chambers, causing ions to migrate towards their respective electrodes. This continuous process ensures high-purity water production without the need for chemical regeneration (Greenlee et al., 2009).

Deionisation with Reverse Osmosis

Many high-purity water production systems combine reverse osmosis (RO) with deionisation to achieve optimal results. This dual-process approach offers several benefits:

1. Comprehensive Purification: RO effectively removes a wide range of contaminants, including dissolved salts, organic molecules, and particles. Deionisation then polishes the RO permeate to remove any remaining ions.

2. Extended Resin Life: By removing the bulk of dissolved solids, RO significantly reduces the load on ion exchange resins, extending their operational life and reducing regeneration frequency.

3. Higher Overall Purity: The combination of RO and deionisation can produce water with extremely low total dissolved solids (TDS) levels, often below 1 ppm (Greenlee et al., 2009).

4. Cost-Effectiveness: While the initial investment may be higher, the combined RO-deionisation system can be more cost-effective in the long run, especially for large-scale applications.

In a typical RO-deionisation system, water first passes through pre-treatment filters to remove larger particles and chlorine. It then undergoes reverse osmosis, where it is forced through a semi-permeable membrane under high pressure, removing up to 99% of dissolved solids. The RO permeate then passes through ion exchange resins or an EDI system for final polishing, resulting in high-purity de-ionised water.

This combined approach is particularly valuable in industries requiring large volumes of high-purity water, such as pharmaceuticals, microelectronics manufacturing, and power generation (Pardue et al., 2018).

Comparing De-ionised Water to Other Purified Waters

De-ionised vs. Distilled Water

While both de-ionised and distilled water are forms of purified water, they are produced through different processes and have distinct characteristics:

1. Purification Method:

   • De-ionised Water: Produced by removing charged ions through ion exchange or electrodeionisation.
   • Distilled Water: Produced by boiling water and condensing the steam, leaving behind most impurities.

2. Contaminants Removed:

   • De-ionised Water: Primarily removes charged ions but may not effectively remove uncharged organic compounds or certain dissolved gases.
   • Distilled Water: Removes a wider range of contaminants, including ions, organic compounds, microorganisms, and most dissolved gases.

3. Purity Level:

   • De-ionised Water: Can achieve very high purity levels, especially when combined with other purification methods.
   • Distilled Water: Generally considered very pure, but may still contain trace amounts of volatile organic compounds that vaporize along with water.

4. Energy Consumption:

   • De-ionised Water: Generally requires less energy to produce compared to distillation.
   • Distilled Water: The distillation process is energy-intensive due to the need for heating and cooling.

5. Specific Applications:

   • De-ionised Water: Preferred in laboratory settings, particularly for analytical chemistry and biochemistry applications where the absence of ions is critical.
   • Distilled Water: Often used in medical applications, automotive cooling systems, and some laboratory procedures where the absence of all impurities is important.

A study by Pardue et al. (2018) found that while both de-ionised and distilled water are suitable for many laboratory applications, de-ionised water is often preferred for its consistency and the ability to produce large volumes more efficiently.

De-ionised Water vs. Reverse Osmosis (RO) Water

Reverse Osmosis (RO) is another common water purification method, often compared to deionisation:

1. Purification Technique:

   • De-ionised Water: Removes ions through ion exchange or electrodeionisation.
   • RO Water: Forces water through a semi-permeable membrane under pressure, removing dissolved solids and other contaminants.

2. Contaminant Removal Efficiency:

   • De-ionised Water: Highly effective at removing charged ions, achieving very low conductivity levels.
   • RO Water: Removes a broad spectrum of contaminants, including ions, organic molecules, and particles, but may not achieve as low conductivity as de-ionised water.

3. Purity Level:

   • De-ionised Water: Can achieve extremely high purity levels, especially when combined with other methods.
   • RO Water: Typically removes 95-99% of total dissolved solids, but may not reach the same purity level as high-quality de-ionised water.

4. Water Recovery Rate:

   • De-ionised Water: Generally has a higher water recovery rate compared to RO.
   • RO Water: Typically has a lower water recovery rate, producing significant wastewater.

5. Maintenance Requirements:

   • De-ionised Water: Requires periodic regeneration or replacement of ion exchange resins.
   • RO Water: Requires regular membrane cleaning or replacement and pre-treatment filter changes.

6. Applications:

   • De-ionised Water: Preferred in laboratory and industrial applications requiring extremely low ion concentrations.
   • RO Water: Widely used in drinking water purification, industrial processes, and as a pre-treatment step for further purification.

Research by Greenlee et al. (2009) indicates that while RO is effective for general water purification, de-ionisation is often necessary for applications requiring ultra-high purity water, such as in semiconductor manufacturing or advanced analytical techniques.

Industrial and Laboratory Applications of De-ionised Water

Laboratory and Research Uses

De-ionised water plays a crucial role in various laboratory and research applications due to its high purity and absence of interfering ions. Some key uses include:

1. General Laboratory Applications: De-ionised water is used for cleaning glassware, preparing reagents, and as a final rinse in many laboratory procedures to prevent contamination from tap water minerals.

2. Clinical Biochemistry and Immunochemistry: In these fields, de-ionised water is essential for preparing buffers, diluting samples, and maintaining the accuracy of sensitive assays. Pardue et al. (2018) found that using de-ionised water significantly improved the reproducibility of enzyme-linked immunosorbent assays (ELISA) compared to tap water.

3. Cell and Tissue Culture Media Preparation: The absence of contaminants in de-ionised water is crucial for creating sterile growth media for cell and tissue cultures. Any impurities could affect cell growth or introduce variables into experiments.

4. Molecular Biology Techniques: De-ionised water is used in PCR reactions, DNA extraction, and other molecular biology procedures where even trace contaminants could interfere with enzymatic reactions or nucleic acid stability.

5. Mass Spectrometry and Spectrophotometry: These analytical techniques require ultra-pure water to ensure accurate results. De-ionised water is used for sample preparation, instrument calibration, and as a blank in many spectroscopic analyses.

Industrial Process Applications

De-ionised water finds extensive use in various industrial processes:

1. Chemical Processing and Manufacturing: Many chemical reactions and processes require water free of interfering ions. De-ionised water is used in the production of pharmaceuticals, cosmetics, and specialty chemicals.

2. Pharmaceutical Production: The pharmaceutical industry relies heavily on de-ionised water for drug formulation, equipment cleaning, and as an ingredient in many medications. The United States Pharmacopeia (USP) sets strict standards for water purity in pharmaceutical applications.

3. Microelectronics Manufacturing: The production of semiconductors and other electronic components requires ultra-pure water. Even minute ionic contaminants can cause defects in microchips. Greenlee et al. (2009) reported that the semiconductor industry often requires water with resistivity greater than 18 megohm-cm, achievable only through advanced deionisation techniques.

4. Food and Beverage Industry: De-ionised water is used in food processing to prevent mineral deposits in equipment, as an ingredient in certain products, and for cleaning and sanitizing.

Cooling Systems and Power Generation

De-ionised water is crucial in cooling systems and power generation:

1. Industrial Cooling Systems: The use of de-ionised water in cooling towers and heat exchangers helps prevent scale buildup and corrosion, improving efficiency and reducing maintenance costs.

2. Boiler Feedwater: Power plants use de-ionised water in boilers to generate steam for turbines. The absence of minerals prevents scale formation on boiler tubes and turbine blades, enhancing efficiency and equipment lifespan.

3. Prevention of Scale Buildup and Corrosion: The low mineral content of de-ionised water significantly reduces scale formation and corrosion in pipes and equipment. This is particularly important in high-temperature and high-pressure systems common in power generation.

Automotive Industry Applications

The automotive industry utilizes de-ionised water in several applications:

1. Engine Cooling Systems: De-ionised water is often used in engine coolants to prevent mineral deposits and corrosion in radiators and engine blocks.

2. Lead-Acid Battery Maintenance: De-ionised water is used to top up lead-acid batteries, as minerals in regular water can shorten battery life and reduce performance.

3. Surface Preparation for Painting and Coating: De-ionised water is used in the final rinse before painting or coating automotive parts to ensure a clean, residue-free surface for better paint adhesion and finish quality.

Specialized Applications

De-ionised water finds use in various specialized applications:

1. Aquarium Water Treatment: Advanced aquarists use de-ionised water to create specific water conditions for sensitive aquatic species or to dilute tap water to achieve desired mineral concentrations.

2. Fire Extinguishing Systems for Electrical Equipment: De-ionised water is used in specialized fire suppression systems for electrical equipment due to its low conductivity, reducing the risk of electrical shock.

3. High-Pressure Cleaning Systems: Industrial cleaning systems often use de-ionised water to prevent mineral deposits on cleaned surfaces, particularly important in industries like aerospace and precision manufacturing.

These diverse applications highlight the critical role of de-ionised water across multiple sectors, from scientific research to industrial manufacturing and specialized technical uses.

Safety Considerations and Drinking De-ionised Water

Potential Health Impacts

While de-ionised water is crucial

Conclusion

De-ionised water plays a vital role across numerous scientific, industrial, and technological applications due to its exceptional purity and unique properties. As this comprehensive overview has shown, the removal of mineral ions through deionisation processes results in water that is crucial for maintaining accuracy in laboratory experiments, ensuring quality in manufacturing processes, and extending the lifespan of industrial equipment.

The diverse applications of de-ionised water - from preparing sensitive cell cultures and calibrating analytical instruments to preventing scale buildup in cooling systems and enabling the production of high-precision electronics - underscore its importance in modern industry and research. Its use spans fields as varied as pharmaceutical production, microelectronics manufacturing, automotive engineering, and power generation. In each of these areas, the absence of interfering ions and contaminants in de-ionised water contributes significantly to process efficiency, product quality, and experimental accuracy.

While de-ionised water is not recommended for regular consumption due to its lack of essential minerals, its value in technical and industrial applications is undeniable. As technology continues to advance, particularly in areas requiring ultra-high purity materials, the demand for and applications of de-ionised water are likely to expand further. Ongoing research and development in water purification technologies, such as improved ion exchange resins and more efficient electrodeionisation systems, promise to enhance the production and quality of de-ionised water, potentially opening up new applications in emerging fields like nanotechnology and advanced materials science. As industries strive for greater precision and efficiency, de-ionised water will undoubtedly continue to be a critical resource, driving innovation and enabling scientific and technological progress.

Key Highlights and Actionable Tips

• De-ionised water is highly purified water with most mineral ions removed, resulting in very low electrical conductivity and neutral pH
• It's crucial for laboratory research, industrial manufacturing, and sensitive equipment operation where water purity is paramount
• Key properties include high purity, low conductivity, neutral pH, and absence of dissolved minerals
• Common production methods are ion exchange, electrodeionisation, and reverse osmosis combined with deionisation
• De-ionised water is preferred over distilled or RO water for applications requiring extremely low ion concentrations
• It's widely used in laboratories, pharmaceutical production, electronics manufacturing, cooling systems, and specialised industrial processes
• While essential for many technical applications, de-ionised water is not recommended for regular consumption due to lack of minerals

How does de-ionised water differ from regular tap water?

De-ionised water has had most or all of its mineral ions removed through processes like ion exchange or electrodeionisation. This results in water with very low electrical conductivity, neutral pH, and almost no dissolved minerals. In contrast, regular tap water contains various dissolved minerals and impurities, giving it higher conductivity and mineral content. The purity of de-ionised water makes it suitable for specialised applications where even trace minerals could interfere with processes or results.

What are the potential risks of using de-ionised water in industrial cooling systems?

While de-ionised water offers benefits in cooling systems by reducing scale buildup and corrosion, there are some potential risks to consider:

1. Increased corrosivity: The lack of minerals can make de-ionised water more aggressive in dissolving metals, potentially leading to corrosion if not properly managed.

2. pH instability: De-ionised water can easily absorb carbon dioxide from the air, forming carbonic acid and lowering pH, which may increase corrosion rates.

3. Microbial growth: The absence of chlorine and other minerals that inhibit microbial growth can potentially lead to increased biological fouling in the system.

4. Cost: Producing and maintaining a supply of de-ionised water for large cooling systems can be more expensive than using treated tap water.

To mitigate these risks, proper system design, regular monitoring, and appropriate chemical treatment programs are essential when using de-ionised water in industrial cooling applications.

How often should ion exchange resins be regenerated in a deionisation system?

The frequency of ion exchange resin regeneration depends on several factors:

1. Water quality: Higher levels of dissolved solids in the input water will exhaust the resins more quickly.
2. Water usage: The volume of water processed affects resin exhaustion rates.
3. Resin capacity: Different resins have varying capacities for ion removal.
4. Required water purity: Systems producing ultra-high purity water may require more frequent regeneration.

Typically, regeneration might be needed every few days to several weeks. However, many modern systems use conductivity monitors to automatically initiate regeneration when water quality drops below a set point. Regular testing of water quality and monitoring of system performance are crucial for determining optimal regeneration schedules.

Can de-ionised water be used in home appliances like steam irons or humidifiers?

De-ionised water can be used in home appliances like steam irons and humidifiers, and it may offer some benefits:

1. Reduced mineral buildup: The lack of minerals in de-ionised water can help prevent scale formation in appliances.
2. Potentially longer appliance life: Less mineral buildup may extend the lifespan of heating elements and other components.
3. Improved performance: In humidifiers, de-ionised water may reduce the release of mineral dust into the air.

However, it's important to consider:

1. Cost: De-ionised water is more expensive than tap water and may not be cost-effective for regular home use.
2. Availability: It may not be readily available in large quantities for home use.
3. Manufacturer recommendations: Always check the appliance manual, as some manufacturers may specify the type of water to use or advise against using de-ionised water.

For most home applications, distilled water or filtered water may be a more practical alternative that still offers reduced mineral content compared to tap water.

What are the environmental impacts of producing de-ionised water on an industrial scale?

The production of de-ionised water on an industrial scale can have several environmental impacts:

1. Energy consumption: Processes like reverse osmosis and electrodeionisation require significant energy input, contributing to carbon emissions if non-renewable energy sources are used.

2. Water waste: Some deionisation processes, particularly reverse osmosis, can have low water recovery rates, producing significant amounts of wastewater.

3. Chemical use: Ion exchange systems require periodic regeneration with acids and bases, which must be properly managed and disposed of.

4. Resin disposal: Ion exchange resins eventually degrade and require replacement, creating solid waste that needs appropriate disposal.

5. Brine discharge: The concentrated mineral solution produced during regeneration or as reject water from RO systems can impact aquatic ecosystems if not properly managed.

To mitigate these impacts, industries are increasingly adopting more efficient technologies, improving water recovery rates, and implementing responsible waste management practices. Additionally, the use of renewable energy sources for powering deionisation systems can help reduce the carbon footprint of production.