The pH of Distilled Water vs. Common Salt

The pH, or potential of hydrogen, is a measure of the acidity or basicity of a solution. Understanding the pH of distilled water and common salt (sodium chloride) is crucial in various applications, from medical procedures to water treatment. In this comprehensive blog post, we will explore the differences in pH between these two substances and their implications.

The pH of Distilled Water

Distilled water, a pure form of water with impurities removed, has a slightly acidic pH, typically ranging from 5.5 to 6.9. This acidity is due to the water’s reaction with carbon dioxide (CO2) in the air, which forms carbonic acid (H2CO3). The formation of this weak acid lowers the pH of the distilled water.

The pH of distilled water can be influenced by several factors:

  1. Exposure to Air: When distilled water is exposed to air, it absorbs carbon dioxide, leading to the formation of carbonic acid and a decrease in pH.
  2. Temperature: As the temperature of distilled water increases, the ionization of water molecules increases, resulting in a higher concentration of hydrogen ions (H+) and a more acidic pH.
  3. Impurities: Even though distilled water is considered pure, it may still contain trace amounts of impurities that can affect its pH.

The pH of Common Salt (Sodium Chloride)

PH of distilled water vs common saltImage source: wikimedia

In contrast to distilled water, common salt (sodium chloride) does not directly affect the pH of water. Sodium chloride is a neutral compound that does not react with water to produce hydrogen ions or hydroxide ions, which are the primary determinants of pH.

However, the addition of salt to water can indirectly affect the pH reading due to the detection of sodium ions (Na+) by the glass electrode used in pH meters. This effect, known as the “salt error,” can lead to a lower pH reading than the actual pH of the solution.

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To minimize the impact of the salt error, it is recommended to recalibrate the pH meter with salt-added samples of reference buffers before measuring the pH of the salt water. This ensures that the pH reading accurately reflects the true pH of the solution.

Implications of pH Differences

The differences in pH between distilled water and common salt have various implications in different fields:

Medical Applications

In medical settings, distilled water is often used for intravenous (IV) solutions and injections due to its pH being closest to that of human blood, which is slightly alkaline (pH around 7.4). The slightly acidic pH of distilled water helps maintain the appropriate pH balance in the body, preventing potential complications.

Water Treatment

In water treatment processes, the pH of the water is a crucial factor. Distilled water, with its slightly acidic pH, may require pH adjustment before being used for certain applications, such as drinking water or industrial processes, to ensure it meets the required pH standards.

Laboratory and Research

In laboratory settings, the pH of distilled water and salt solutions is essential for various experiments and analyses. Accurate pH measurements are crucial for maintaining the integrity of experimental results and ensuring the reliability of scientific data.

Industrial Applications

The pH of water and salt solutions can impact various industrial processes, such as electroplating, chemical reactions, and water purification. Monitoring and controlling the pH in these applications is crucial for ensuring product quality, process efficiency, and environmental compliance.


In summary, the pH of distilled water and common salt (sodium chloride) differ significantly. Distilled water has a slightly acidic pH due to its reaction with carbon dioxide in the air, while common salt does not directly affect the pH of water. Understanding these differences and their implications is essential in various fields, from medical applications to industrial processes. By considering the pH of these substances, professionals can make informed decisions and ensure the optimal performance and safety of their respective operations.

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