Distilled Versus Demineralised Water in Electroplating Processes: Differences, Characteristics and Applications

Water is one of the most critical factors in the electroplating industry, where precision and repeatability of processes are paramount for coating quality. The proper selection and control of water parameters directly impact the efficiency of aluminium anodising, metal blackening, galvanic zinc plating, and chrome plating. In machining processes such as CNC cutting and milling, water quality also plays a significant role – the appropriate dilution of coolants prevents sediment buildup and extends machine durability.

These technologies – from aluminium anodising to blackening, zinc plating, and chrome plating – require water with precisely defined properties. Two terms frequently arise in this context: distilled water and demineralised water. At first glance, these two types of water may seem almost identical, but in practice, they differ in production methods, chemical composition, and applications. In electroplating processes, even the smallest differences in purity or ion content can result in significant variations in the quality and durability of the coatings produced.

This article takes a closer look at the characteristics of distilled water and demineralised water, as well as their applications in the electroplating industry. Understanding when to use distilled water versus when demineralised water is the better choice not only helps optimise the coating process but also reduces equipment operating costs. This topic is directly connected to issues discussed in our previous blog posts, where we explored various coating techniques (e.g., galvanic zinc plating, metal blackening), CNC machining processes, and maintaining high-quality electroplating baths.

By adopting a comprehensive approach to the issue of “distilled water vs demineralised water” in the context of surface treatment, we gain a full understanding of how such an apparently “ordinary” element can profoundly influence the final result. Properly selected and purified water eliminates unwanted residues, ensures a uniform coating structure, and provides long-lasting corrosion protection for treated parts. As a result, this increases the reliability and lifespan of galvanised components and positively impacts the efficiency of the entire production line.

In the subsequent sections of this article, we will delve into the differences in how these two types of water are produced, compare their fundamental properties, and demonstrate how to use them effectively in electroplating and CNC processes to achieve the best possible results.

How Is Distilled and Demineralised Water Produced?

To understand why distilled and demineralised water differ in their applications within electroplating processes, it is essential to closely examine their production methods. Although the end result—water of high purity—is similar in both cases, the processes themselves differ in technology, cost, and the range of impurities they remove.

Distilled water – a technology with a long tradition

Distillation is one of the oldest and simplest methods for obtaining water of nearly perfect purity. The process involves heating water to its boiling point to turn it into steam and then condensing that steam in a separate container. As a result of this operation, the vast majority of ions, mineral salts, and other substances remain in the boiler (in what is known as the residue after evaporation).

• Principle of operation:
  1. Raw water (e.g., tap water) is fed into the distillation device.
  2. Steam is generated by heating the water.
  3. The steam passes through a cooling system (condenser), where it undergoes condensation.
  4. The condensed water is collected in a container for distilled water.
• Main advantages of distillation:

• • High level of purity – almost all ions and many solid impurities are removed.
  • Versatile application – distilled water is ideal for environments requiring absolute sterility or the absence of any chemical influence on the process (e.g., laboratories or certain stages of electroplating).

• Limitations and costs:

• • Energy-intensive – heating, evaporating, and condensing water requires a significant amount of energy, leading to high operational costs.
  • Time-consuming – the evaporation and condensation process takes time, making it less efficient for producing large quantities of liquid.

In the context of electroplating processes, distilled water is used in the most demanding operations where even trace impurities could affect the stability of the plating bath or the quality of the resulting coatings. This is especially true in producing extremely delicate layers (e.g., during certain types of anodising) or in the final rinsing stage of components requiring a perfectly clean surface.

 

Demineralised Water – Economy and Modern Technologies

In contrast, demineralised water is produced using more advanced chemical and physical methods, aimed at removing mineral ions (such as calcium, magnesium, iron, or sodium) as well as other impurities, including certain organic substances. Two technologies are most commonly used (often combined in a single system):

1. Reverse Osmosis (RO)
   • The process involves forcing water through a semi-permeable membrane under high pressure.
   • The membrane blocks larger particles and ions (e.g., heavy metals, mineral salts), allowing only water molecules to pass through.
   • This results in two streams: permeate (purified water) and concentrate (containing concentrated impurities).
2. Ion Exchange
   • A chemical method that replaces ions dissolved in water with hydrogen (H⁺) or hydroxide (OH^–) ions.
   • This is achieved using ion exchange resins (cationic and anionic), which selectively “capture” unwanted ions.
   • The resulting water has a very low mineral ion content, preventing sediment formation in subsequent processes.

• Main advantages of demineralisation:
  • Lower energy consumption – compared to distillation, methods such as reverse osmosis and ion exchange require significantly less energy.
  • High throughput – with appropriate modules, large quantities of high-purity water can be produced in a relatively short time.
  • Flexibility – the level of demineralisation can be tailored to specific needs (e.g., using more than one ion exchange column to achieve ultra-low conductivity water).
• What may remain in demineralised water?
  • Trace amounts of organic compounds (especially volatile ones) that were not retained by the membrane or resin.
  • Dissolved gases, such as carbon dioxide or oxygen.

In the electroplating industry, Cesium demineralised water is often chosen as an optimal compromise between required purity and treatment costs. It works excellently in baths for zinc plating, blackening, or chrome plating, where eliminating water hardness is critical, but extremely low levels of all possible contaminants are not necessary (as in electronics manufacturing or research laboratories). Additionally, the lower operating costs of demineralised water translate into more affordable coating and treatment processes, which is crucial in mass electroplating production.

 

Trends and the Future of High-Purity Water Production

In an era of growing ecological awareness and the need to conserve resources, increasing attention is being paid to:

• Water recycling – recovering water from electroplating processes (rinsing, baths) and re-treating it using a combination of filtration, reverse osmosis, and ion exchange.
• Integrated monitoring systems – modern measurement systems allow real-time control of conductivity, pH, and chemical content, minimising the risk of introducing water that does not meet requirements into the production line.
• Hybrid technologies – combining membrane and ion exchange methods in a single system, often enhanced with UV disinfection or ozonation, ensuring extremely low microorganism concentrations.

All these advancements are particularly significant for electroplating plants aiming to maintain stable process parameters, high-quality coatings, and simultaneously minimise media consumption costs. A conscious choice between distilled or demineralised water should always be guided by specific technological requirements and a long-term cost-effectiveness analysis.

Differences in Physicochemical Properties

Comparison of Distilled and Demineralized Water in Galvanic Processes
Parameter	Distilled Water	Demineralized Water	Significance in Galvanic Processes
Treatment Method	Distillation (heating to boiling, condensation of vapor)	Reverse osmosis, ion exchange (or combination of both)	The choice of technology affects the type and amount of impurities remaining in the water. In later stages of galvanic processes, it often determines the purity of baths or rinses.
Mineral Salt Content	Very low (practically trace amounts as a result of condensing pure vapor)	Very low, but some inorganic and organic trace compounds may remain, depending on the quality of membranes and resins	Minimal salt content prevents the formation of deposits (e.g., in zinc plating or blackening processes). In cases requiring absolute purity (e.g., advanced anodizing), distilled water can ensure fewer micro-impurities.
Electrical Conductivity	Usually very low (even < 1 µS/cm), though it can increase upon contact with air (dissolution of CO2)	Depends on the degree of filtration applied. Typically 0.2–5 µS/cm (with the possibility of achieving lower values in multi-stage systems)	Low water conductivity helps maintain stable electrolysis conditions and limits unwanted side reactions. The lower the conductivity, the smaller the risk of introducing “foreign” ions into the galvanic bath.
pH	About 5.0 (slightly acidic) Influence of dissolved CO2	Can range from 5 to 7.5 Depends on the quality of the reverse osmosis process and degree of deionization	The pH of the water affects the electrolyte balance in the galvanic bath (e.g., in aluminum anodizing, strictly controlled acidity is required). Slight pH deviations can determine the quality and uniformity of the protective layer.
Presence of Organic Compounds	Minimal, as most volatile organic substances do not condense at water’s boiling temperature However, minimal amounts of volatile impurities may remain	Depends on the quality and type of membranes (RO) and ion-exchange resins Organic compounds may slightly permeate through membranes	High concentrations of organic compounds in baths could affect electrochemical properties, especially when forming decorative or protective coatings. This is significant in processes requiring ideal surfaces, such as chroming for decorative purposes.
Impact on Galvanic Equipment	Minimizes the risk of corrosion and scale formation However, it may generate higher production and transportation costs (high energy consumption)	Equally effectively prevents scale deposition Production processes are usually less energy-intensive and more cost-effective on a large scale	In mass production (e.g., zinc plating of automotive components), both the quality and the cost of obtaining water are important. For highly specialized processes (e.g., micro-galvanization in electronics), distilled water is often preferred.
Target Applications	Laboratories, pharmaceutical industry Advanced galvanic processes with critical purity requirements	Automotive, electronic, textile industries Galvanic applications with medium or high sensitivity to mineral ions	The key criterion for choosing between distilled and demineralized water is the specificity of the process: desired level of purity vs. cost-effectiveness. For smaller companies and mass production lines, demineralized water often provides sufficient quality at relatively lower costs.

As highlighted in the above comparisons:

• Distilled water stands out for its minimal content of inorganic impurities as well as most organic compounds and dissolved gases. However, achieving such high purity comes with higher costs (energy consumption, limited efficiency).
• Demineralised water is more economical for mass use, and its purity level is sufficient for the vast majority of electroplating processes where the primary requirement is the elimination of salts and mineral ions responsible for water hardness.

For tasks involving advanced surface treatment – such as aluminium anodising or creating highly decorative chrome coatings – water with near-zero levels of unwanted compounds may be necessary. On the other hand, for a wide range of typical electroplating operations (e.g., galvanic zinc plating of large batches of steel components), demineralised water will generally be sufficient and more cost-effective.

However, it is important to remember that even minimal differences in water composition can impact the stability and performance of electroplating solutions. Therefore, when choosing a specific option (distilled or demineralised), it is crucial to consider the precise process requirements, including costs, production scale, and the desired degree of purity.

Application in the Electroplating Industry

In the context of broadly understood electroplating processes – such as aluminium anodising, metal blackening, galvanic zinc plating, or chrome plating – distilled and demineralised water play a crucial role in ensuring the desired quality of coatings. Each of these electroplating methods requires specific bath parameters, and even trace amounts of mineral ions or organic compounds can significantly impact the durability, appearance, and functionality of the resulting layers. Equally important is the proper dilution of coolants in CNC machines, which often form an integral part of the technological line in facilities performing surface treatment.

Aluminium Anodising

• Precise Control of Electrolyte Composition During aluminium anoding , the electrolyte (usually an acid solution) is fundamental, and the purity level of the water plays a critical role. The presence of unwanted ions or dissolved salts could disrupt the process of forming a uniform oxide layer.
• Distilled Water in the Rinsing Stage After removing the part from the anodising bath, thorough rinsing with distilled water removes electrolyte residues from the pores of the newly formed oxide layer. This prevents contaminants from affecting the final colouring or corrosion resistance.
• Demineralised Water – An Economic Compromise In many anodising facilities, especially those handling larger-scale production processes, demineralised water (with appropriately low electrical conductivity) is used. The advantage is lower cost while maintaining parameters sufficient for most standard anodising applications.

Metal Blackening

• Stability of Blackening Baths metal blacking (particularly steel) involves creating a thin oxide layer that provides corrosion protection and an aesthetic effect. The presence of iron, calcium, or chlorine ions in the water can lead to unwanted deposits on the surface or even cause corrosion pitting.
• The Role of Water in Cooling and Rinsing Both distilled and demineralised water play a crucial role in rinsing components between different stages of the blackening process. This prevents the transfer of unwanted contaminants that could degrade the adhesion and durability of the coating.
• Costs vs. Quality Requirements For mass production, where blackening serves as a protective step, demineralised water is usually sufficient. However, in cases where a very high-quality finish is required (e.g., for exposed components or precision products), distilled water can provide additional protection against micro-contaminants.

 

Galvanic zinc plating

• Preventing Deposits in Zinc Plating Bath electroplating of zinc is widely used in the automotive and machinery industries to protect steel components from corrosion. The presence of salts in the water can lead to unwanted precipitates, resulting in dullness or uneven coating distribution.
• Demineralised Water in Large-Scale Production Due to the high volumes of zinc plating, demineralised water is predominantly used, as the cost of producing distilled water on such a scale would be prohibitive. In most cases, the achieved water purity (with controlled conductivity levels) is sufficient to maintain stable parameters in the zinc plating bath.
• Importance of Rinsing Processes To prevent contamination of freshly zinc-coated surfaces with electrolyte residues or unwanted ions, the industry employs multi-stage rinsing systems. Each stage often uses water with varying levels of purity – ranging from demineralised water to water with parameters close to distilled.

Chrome Plating

• Reactions in Acidic Environments chrome plating is another process that requires precise control of bath composition, often based on chromium compounds (Cr³⁺ or Cr⁶⁺). The presence of calcium, magnesium, or sulphate ions can disrupt electrolytic reactions, leading to coating defects such as pores or flaking.
• Distilled Water for Decorative Coatings High gloss and perfectly smooth surfaces are critical outcomes for manufacturers, particularly in industries such as household appliances, automotive, or design. For these demanding applications, distilled water is often preferred as it nearly eliminates the introduction of unwanted ions that can cause micro dullness.
• Use of Demineralised Water in Smaller Businesses Smaller facilities that perform chrome plating on less demanding components (e.g., technical parts not visible to the user) often opt for demineralised water, reducing costs while maintaining adequate coating quality.