Water purification processes remove impurities, offering various grades of water suitable for specific needs. Understanding the distinctions between different types of purified water, such as deionized and distilled, is important. This article clarifies the distinctions between deionized and distilled water and their appropriate applications.
Distilled Water Explained
Distilled water is produced through a process that mimics the natural hydrological cycle: boiling and condensation. Water is heated to create steam, leaving behind most impurities in the boiling chamber. This steam then cools and condenses back into a liquid state, which is collected as distilled water.
This purification method removes a broad range of contaminants. It removes inorganic compounds like minerals, salts, and heavy metals, as well as large non-volatile organic molecules. The boiling process also inactivates microorganisms such as bacteria, viruses, and protozoan cysts. However, volatile organic compounds (VOCs) with boiling points similar to or lower than water might vaporize along with the water, potentially re-contaminating the distilled product.
Deionized Water Explained
Deionized water, often called demineralized water, undergoes a process that primarily targets dissolved mineral ions. This purification typically involves passing water through ion-exchange resins. Cationic resins exchange positively charged ions (cations) like sodium, calcium, and iron for hydrogen ions, while anionic resins exchange negatively charged ions (anions) such as chloride, sulfate, and carbonate for hydroxide ions.
The hydrogen and hydroxide ions then combine to form water molecules, removing most dissolved mineral salts. This process is effective at removing charged impurities. However, deionization does not effectively remove uncharged contaminants, including non-ionic organic compounds like sugars or alcohols, or biological impurities such as bacteria and viruses.
How They Differ
The primary distinction between distilled and deionized water lies in the types of impurities each purification method targets and removes. Distillation relies on phase change, separating water from substances that do not vaporize easily, while deionization specifically removes dissolved ions through chemical exchange. Consequently, distilled water is generally free of both ionic and non-volatile organic contaminants, along with microorganisms. Deionized water, conversely, excels at removing ions but may still contain uncharged organic molecules, bacteria, or viruses.
Purity levels also vary, particularly concerning electrical conductivity. Deionized water exhibits extremely low conductivity because it has been stripped of conductive mineral ions. Distilled water also has low conductivity due to the removal of most dissolved solids, but it might retain slight conductivity from dissolved gases or trace volatile compounds that can co-distill.
Where Each is Used
The characteristics of distilled and deionized water make them suitable for specific applications. Distilled water is used in medical settings for sterilizing equipment and in kidney dialysis machines, where the absence of minerals prevents residue buildup and ensures purity. It is also used in automotive applications, such as car batteries and cooling systems, to prevent corrosion and mineral deposits. In households, distilled water is used in humidifiers and steam irons to avoid mineral scaling.
Deionized water is used in industries requiring water free of mineral ions. It is used in electronics manufacturing for rinsing sensitive components, pharmaceutical production, and laboratory settings where ion-free water is necessary for accurate experimental results. It also prevents scale formation and ensures operational efficiency in cooling systems and industrial machinery cleaning. While both types of water are purified, deionized water is generally not recommended for drinking due to its lack of beneficial minerals and its tendency to leach minerals from the body and piping systems.