The difference between distilled and deionized water is in the way that they are produced and the quality of the output water. Both produce types of pure water, but depending on the end use, the type of purity matters.  Purified water is required for a wide variety of uses including industrial, medical and home use.  The type of purification used will depend on the properties needed so it is necessary to understand the difference between distilled and deionized water.

| Production of distilled vs deionized water

Many people start with the question “Is deionized water the same as distilled water”?  The answer to that is no, as they vary in the types of contaminants removed as well as in method and cost.  Both deionized water and distilled water are examples of water that has been processed to result in a high level of purity.

Deionized water focuses on removal of inorganic compounds such as salts and other minerals.  To achieve this, water is passed across special resins containing both cations and anions.  The properties of the cations and anions allow for capture of oppositely charged atoms and results in non-ionized molecules of pure water.  The process is very effective for removing almost all inorganic contaminants but must be filtered through a different media prior to deionization to remove organic compounds.

Distilled water uses heat, evaporation and condensation to remove both organic and inorganic compounds.  Contaminated water is heated until it reaches the evaporation point as steam.  The steam is then captured in a sterile container or hood overhead where it condenses back into water and is shunted to yet a different container.  While both remove inorganic contaminants, distillation removes organic material as well and requires no additional filter media prior to distillation.

Water Distillation
Water Distillation

Deionized Water System – Single PS-300

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| Deionized Water Uses and Applications

Deionized water is used primarily for laboratory, medical and industrial uses.  Home use and human consumption is possible and can be used in most applications where distilled water is used, although it is less common to do so.  Deionized water is ideal for applications such as injection systems or atomizers where regular water may leave behind a buildup of particulate matter that clogs nozzles and hamper performance of equipment over time.  It is also used in applications where biological or sterile fields are required.  And in cases where the chance of electrical conduction needs to be reduced, deionized water’s balanced ions can be useful as well.  For most industrial and medical use, cartridge based deionized water systems can be installed using the building’s water supply to produce deionized water on site. If smaller quantities are needed then you can buy deionized water in containers, but shelf life has to be considered,

Here are a few of the most suitable uses for deionized water:

  • Cooling Systems – Deionized water is ideal for high tech uses such as cooling for high powered lasers. The low conductivity allows a higher safety factor as well as high purity.  It is also used in automobile engines as a top off in radiators.
  • Battery Systems – Deionized water is used in lead acid batteries for auto engines and electrical vehicles such as forklifts batteries. It can lengthen the life of the battery due to its lack of ions.
  • Laboratory Testing – There are two major advantages of using deionized water in laboratory environments. One is that given testing often deals in measuring minute particulates as part of the test, any unwanted particulate matter, no matter how small, can affect the outcome of the test.  Two, deionized water can be used to clean instruments within the lab without leaving any inorganic contaminants on the instrument because of the cleaning.
  • Industrial Equipment – Due to wear and tear, ambient environmental conditions within a factory and other related issues, industrial equipment requires regular cleaning. Regular water could leave behind particles that would encourage corrosion within the equipment.  Deionized water allows for thorough cleaning while reducing the chance of harmful particulate matter being left behind.  It is also ideal for improving quality in manufacturing processes where water is used to cool or lubricate parts as they are produced.
  • Service Industries – Service industries such as home and commercial window cleaning use deionized water to eliminate residue that leaves smears on rinsed windows after cleaning.


There are other uses such as fire extinguishers and aquariums where deionized water is useful as well.  In the former, the water’s low conductivity aids in situations where a water-based extinguisher might be used near electrical components.  In the latter, the high level of purity and aids in the inhibition of algae growth.  It is also used extensively in the production of electronic circuits as a final rinse after processing to remove alkalis and acids.

| Distilled Water Uses and Applications

Like deionized water, distilled water is used for laboratory, medical and industrial uses but also has extensive use in service industries such as cleaning.  Distilled water is also used more often within homes compared to deionized water.  It is excellent for appliances and applications where atomizers and misters may clog using regular water.  It is also ideal for specific medical requirements that are hyper vigilant about organic material when sterilizing instruments and equipment.

Here are a few of the most suitable uses for distilled water:

  • Medical – Distilled water is used extensively within the medical field. When conditions such as surgical preparation require no organic material be left on a professional’s hands prior to performing a procedure, distilled water can provide such assurance.  It is also used in vapor or irrigation equipment such as CPAP machines, humidifiers, Neti Pots and other systems where the water will contact the patient as part of the treatment.
  • Laboratory Testing – Like Deionized, distilled water is used in laboratory testing. It is used to clean as the absence of both inorganic and organic materials mean that instruments will not “spot” when dry.  It is also used to guarantee the purity of the test and eliminate contamination of samples and the skewing of results based on impurities within water.
  • Food Industry – Distilled water is used extensively within the food industry, especially in canning. The use of distilled water can reduce build up and cloudiness in containers.  It also prevents particles from leeching into the food after it is preserved and maintain taste and health quality.  Regular water can impart any particles within the food and toughen the food or impact its safe consumption.
  • Cosmetics Industry – Similar to the reasons for use within the food industry, the cosmetics industry relies upon distilled water as well. It assures that no organic matter is present to promote the growth of bacteria.  And, the lack of inorganic matter eliminates the chance of inorganic compounds interacting with compounds in the cosmetic to produce off quality or even harmful effects.
  • Home Use – Distilled water is also used more extensively within the home than deionized water. One common use is for cooking.  Depending on the makeup of tap water, regular water can contain acids, alkalis, and other minerals that can discolor or affect the taste of food.  It is also commonly used in the home in appliances such as steam irons and plant misters where atomized water is required and where regular water could clog the nozzle over time.

| Pros and Cons between distilled vs deionized water

While both purification methods have numerous industrial and home applications, there are pros and cons to consider for each.  It is important to understand the individual pros and cons when evaluating the difference between distilled vs deionized water:

Comparison Distilled vs Deionized Water
Comparison Distilled vs Deionized Water

Deionized Water


  • Reliably removes inorganic matter.
  • Inexpensive compared to other methods of purification.
  • Resins can be recharged for extended use.
  • Low electrical resistance


Distilled Water


  • Reliably removes organic matter, bacteria and viruses.
  • Removes soluble minerals such as calcium, magnesium, and phosphorous and reduces scaling.
  • Will remove heavy metals such as mercury, lead and arsenic.


  • May retain synthetic chemical particles if the chemical has a lower boiling point than water (pesticides, herbicides).
  • High cost to set up and operate

| Conclusions

Distilled and deionized water difference results not only from the method used to produce them but in what type of contaminants they remove as well.  In some cases, the requirement may go beyond the choice between deionized water vs distilled water as applications may require the use of “ultrapure” water.  This process may be achieved by passing deionized water across a Reverse Osmosis (RO) membrane to remove any remaining ions as well as other large molecules from the water.  It is also possible to produce ultrapure water by utilizing both deionization and distillation to achieve the highest level of purity.

Both deionized and ionized water have many uses.  And while they are interchangeable in some applications, the difference in what materials are removed is a factor in selecting the purification method with the correct characteristics.

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