Deionized Water vs Distilled Water

I often have teachers ask me questions regarding laboratory water. What’s the difference between DI water and distilled water? Can I use either one in the lab? Are they the same, and are they interchangeable? Let’s talk pure water! I’ll answer your questions and give some recommendations for setting up the water supply for your labs depending on budget and size of your science department.

What’s the difference between DI water and Distilled water?

Deionized (DI) water and distilled water are both types of purified water, but they are produced through different methods, resulting in slight differences:

Deionized Water (DI Water):

Production Method:

  • Deionized water is water that has had its mineral ions (such as calcium, magnesium, sodium, and chloride) removed through an ion exchange process.
  • This process involves passing water through ion exchange resins or membranes to remove ions, such as calcium, magnesium, sodium, and chloride ions.
  • Passing water through resins that exchange ions for hydrogen and hydroxide ions, effectively remove dissolved ions from the water.

Purity: DI water typically has low conductivity and is free from most ions, but it may still contain non-ionic impurities.

Applications: DI water is commonly used in laboratories, industrial processes, and electronics manufacturing where the presence of ions could interfere with chemical reactions or damage sensitive equipment.

Distilled Water:

Production Method:

  • Distilled water is produced by boiling water and then condensing the steam back into liquid form.
  • During the distillation process, impurities, including minerals, metals, and most microorganisms and contaminants, including mineral ions, are left behind as the steam is collected and condensed.
  • This process effectively removes not only minerals but also most other impurities, resulting in very pure water.
  • Distilled water is often used in laboratories, medical settings, and in household appliances like steam irons and humidifiers.

Purity: Distillation removes both ionic and non-ionic impurities, making it more thorough in purification compared to deionization. Distilled water is one of the purest forms of water available.

Applications: Distilled water is commonly used in laboratories, medical facilities, and in household appliances like steam irons and humidifiers. It is suitable for applications where high purity and an absence of organic material is required.

Key Differences:

  • Deionized water primarily removes mineral ions, while distilled water removes a broader range of impurities through the distillation process.
  • Deionized water may still contain non-ionic impurities, while distilled water is virtually free from all impurities.
  • Deionized water tends to be more conductive than distilled water due to the presence of ions, although both are considered highly pure compared to tap water or other sources.

Can I use Distilled water instead of DI water?

In most cases, distilled water can be used as a substitute for deionized (DI) water in high school laboratory applications, especially if the specific requirements for ultra-purity are not necessary. However, there are some considerations to keep in mind:

Laboratory Use: Some experiments or procedures, such as prepping solutions, may require the complete removal of ions to prevent ion interference in the results. In such cases, either DI water or distilled water are appropriate.

How does DI water and distilled water compare in terms of cost and efficiency?

Cost and Availability: If the laboratory budget is a concern, you will probably want to go with deionized water. A demineralizer (deionizer) can be purchased for around $1500.00 without cartridge. The cartridges run around $200.00. The cartridges will demineralize about 75 gallons, or about 285 L , before needing replacement. One demineralizer can serve a large science department easily.

A water still can run anywhere around $2500.00, or more, depending on the unit. Even though a water still does not have a cartridge that needs replacing, the up front expense is about double. Of course, if you are in a small science department, you can purchase distilled water in gallon jugs.

Comparing Efficiency: The Barnstead Bantam demineralizer delivers approximately 10 gallons per hour. Filling a 20 L carboy of DI water is pretty easy. Whereas the water still delivers around one gallon/hour.

In summary, while both deionized and distilled water are forms of purified water, they are produced using different methods and offer different levels of purity. Distilled water is typically purer than DI water because it removes both ionic and non-ionic impurities through the distillation process. The choice between DI water and distilled water depends on the specific requirements of the application and the desired level of purity. For the high school chemistry lab, though, DI water is most commonly used due to its efficiency in cost and production. However, distilled water can be substituted in the high school chemistry lab without problem.

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