While both distilled and demineralized water undergo purification, they are distinct. Understanding their differences requires examining how each is produced and the specific contaminants each method targets.
What is Distilled Water?
Distilled water is created through a process of boiling and condensation. Water is heated to its boiling point, turning into steam. This steam then rises, leaving behind most non-volatile impurities such as minerals, salts, heavy metals, and many organic compounds in the boiling chamber. The purified steam is then collected and cooled, condensing back into liquid water.
This method effectively removes a broad range of contaminants, including bacteria, viruses, and dissolved solids. While distillation yields highly pure water, some volatile organic compounds with lower boiling points than water might vaporize along with the water and re-condense, meaning the final product is not absolutely free of all impurities.
What is Demineralized Water?
Demineralized water, often referred to as deionized water, is produced by removing dissolved mineral ions. This purification typically involves passing water through ion-exchange resins. These resins attract and bind to positively charged ions (cations like calcium, magnesium, and sodium) and negatively charged ions (anions like chloride, sulfate, and nitrate), exchanging them for hydrogen and hydroxide ions.
The hydrogen and hydroxide ions then combine to form pure water. While this process is highly effective at removing ionic impurities, it generally does not remove non-ionic substances such as organic compounds, bacteria, or viruses.
Comparing Purity and Process
The fundamental difference between distilled and demineralized water lies in their purification methods and the impurities they target. Distillation, a physical process, removes a broad spectrum of impurities including minerals, microorganisms, and many organic materials, resulting in water with very low dissolved solids and biological contaminants. Demineralization, a chemical ion-exchange process, excels at removing dissolved mineral salts, leading to extremely low conductivity. However, demineralized water may still contain non-ionic impurities like organic compounds, bacteria, or viruses. While both are purified, distilled water generally achieves a broader removal of contaminants, making it “purer” in a more comprehensive sense, especially regarding non-ionic substances and microbes.
Practical Applications
Each type of purified water serves specific purposes based on its distinct characteristics. Distilled water’s broad purity makes it suitable for applications where nearly all impurities must be absent. It is commonly used in medical and laboratory settings, for diluting solutions, and in medical devices like CPAP machines to prevent mineral buildup and ensure hygiene. Its use extends to car batteries, steam irons, and humidifiers, where mineral-free water prevents scaling and corrosion, extending appliance lifespan.
Demineralized water finds extensive use in industrial processes where the absence of mineral ions is paramount to prevent scaling or interference. This includes cooling systems, electronics manufacturing, and certain pharmaceutical processes, particularly for equipment cleaning where ionic contamination would be detrimental. For instance, power plants rely on demineralized water to prevent mineral deposits in turbines and boilers, which can significantly impair efficiency and cause damage.