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Ultrapure, deionized, RO, distilled and double distilled waters: What Is The Difference?

In wastewater treatment, we often encounter water quality requirements which can be indicated with various terms, such as ultrapure water, deionized water, RO water, distilled water, and double distilled water.

But, what do they really mean?

In this short article YASA ET's engineers share their knowledge by answering the following questions:

  1. What do those water standards mean?

  2. How to distinguish them?

  3. How do they affect your projects?


01 Ultra-pure water

Ultrapure water: in ultrapure water, not only the conductive medium in the water is almost completely removed, but also keeps the non-dissociated colloidal substances, gases and organic matter in the water to a very low level.

Usually NANOpure or Milli-Q is commonly used in the laboratory, and the water source is generally deionized water or RO water.

02 Deionized water

Deionized water: water without anions and cations in the water. The ions in the water are mainly removed by RO membranes and a mixed bed resin. Commonly used water generators include MilliporeElix, but there are still soluble organic matter, such as heat sources, so deionized water is generally not used as water for injections.

03 RO water

RO water: also known as pure water. That is, the water filtered through the reverse osmosis membrane, the pore size of the reverse osmosis membrane is generally between 10A and 100A, so it can remove more than 95% of ionic impurities.

04 Distilled water

Distilled water: The water obtained by using the difference in the volatility of the components in the liquid mixture to vaporize H2O and then partially condense and separate the vapor.

It can remove most of the pollutants in the tap water, but the volatile impurities cannot be removed, such as carbon dioxide, ammonia, silicon dioxide and some organic matter. Fresh distilled water is sterile, but bacteria can easily multiply after storage.

05 Double distilled water

Double distilled water: Distillation-DistillationH2O is the water obtained after two distillations.

The water contains very low inorganic salts, organic matter, microorganisms, soluble gases and volatile impurities, and removes the heat source. Generally, it can be used for water for injections.

Water Purity Comparison

The water order based on purity level:

Ultrapure > Deionized > Double Distilled (ddH2O) > Pure (RO) > Distilled

Ultrapure water can be used as all experimental water, especially high-sensitivity ICP/MS, ppt level analysis, isotope analysis, CDC, drug inspection institute, quality inspection institute, environmental monitoring station, university scientific research and other standard laboratories and various Water for high-end precision instruments.

Other pure water and double distilled waters can also be used when the requirements are not very strict according to actual applications conditions.


Contact Us

YASA ET cooperate with many companies in different industries, including ZF, Schaeffler, ABNEN and many others for their wastewater treatment projects.

Our customers cover multiple industries and fields such as auto parts manufacturing, surface treatment, semiconductors, bearings just to name a few. In all these projects, we solved their emulsion, electroplating and salty wastewater treatment problems, and help them reduce the environmental impact caused by their industrial production.

For more information, kindly get in touch with our team:



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The content of this article is compiled and released by YASA Environmental Technology based on network data. If there is any infringement, please contact the author. Extra sources: Water quality - Wikipedia


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