This means that it typically needs to be used in tandem with another type of treatment, such as Reverse Osmosis, to ensure that all contaminants are properly eliminated from it. It is the assumption that because distilled water has been purified, it has a neutral pH of 7. D.I. Water. The Relationship between pH and Deionized Water . Deionized water is free of ions, which are charged molecules or atoms that occur naturally in water. What is distilled water? As soon as water comes in contact with air, CO2 gas starts to dissolve it, forming carbonic acid (H2CO3). The topic of pH and water has been well documented over the years; however, there is still much confusion about its significance in high purity water applications. To determine the pH of **D.I 3. *That test will produce a score from 1 to 14. To measure the pH of water accurately you will require pH Ionic Strength Adjusters. The basics of pH . In practice, it’s difficult to put an exact number on the pH of distilled water because simple exposure to air can dissolve carbon dioxide.. Why does the pH of a substance matter? This results in the pH being lower than seven. The pH scale encompasses 14 orders of m agnitude of the concentration of the Hydrogen (H+) ion on a scale of 0 to 14. * water, it is necessary to conduct a test using the pH scale, which measures whether or not a substance is an acid, a base or neutral 1. But this is not always the case because distilled water is very rarely 100% pure, and even more rarely has a pH … You must also keep in mind that water (Deionised Water, or Distilled Water) do not have a pH of 7. The pH of distilled water is theoretically about 7. Deionized water, like distilled water, is a very pure form of water. Where they differ is that deionized water is water that has had all the ions removed from it.