Tap water, whether sourced from the ground or a municipal system, contains various dissolved solids, minerals, and contaminants requiring treatment before consumption or use. Purified water and distilled water are two distinct methods for achieving high levels of cleanliness from this source water. While both processes result in water far cleaner than standard tap water, they employ fundamentally different mechanisms that affect their final composition and intended purpose. Understanding these technical differences is necessary to determine which type of water is best suited for a particular need.
How Water Becomes Purified
The creation of purified water involves a multi-stage process starting with source water, such as tap water or groundwater. This process relies on mechanical and chemical methods designed to strip away virtually all chemicals, suspended particulates, and microorganisms. The primary method is Reverse Osmosis (RO), where water is forced under pressure through a semi-permeable membrane that blocks larger molecules, effectively removing a majority of contaminants and dissolved salts.
Following RO, the water often undergoes further refinement, such as passing through carbon filters to remove trace organic compounds, odors, and tastes. Another element is deionization (DI), which uses ion-exchange resins to chemically swap contaminant ions for hydrogen and hydroxyl ions, combining to form pure water. The final product must meet a rigorous standard set by the United States Pharmacopeia, requiring the Total Dissolved Solids (TDS) to be reduced to no greater than 10 parts per million (ppm).
How Water Becomes Distilled
Distillation, unlike purification’s multi-step filtration, is a thermal process utilizing a simple phase change to separate water from its impurities. The process involves boiling the source water to generate steam, which leaves behind non-volatile substances like heavy minerals, salts, and most bacteria. The clean steam is then collected and cooled in a separate chamber, where it condenses back into liquid water.
Because this method relies on contaminants not vaporizing with the water, it is extremely effective at removing dissolved solids and non-volatile impurities. However, distillation may allow volatile organic compounds (VOCs), which have a lower boiling point than water, to vaporize along with the steam. Trace amounts of these specific contaminants can remain in the final product.
Compositional Differences and Taste
The fundamental difference between the two types lies in the resulting chemical profile, largely measured by the TDS level. Both purified and distilled water are characterized by extremely low TDS. Commercial purified water often achieves its final state through a blend of technologies that can address a broader range of contaminants, including volatile ones. Both processes aggressively remove naturally occurring minerals, such as calcium and magnesium.
The removal of these dissolved minerals heavily influences the water’s flavor, resulting in what many describe as a “flat” or “empty” taste for distilled water. This lack of flavor is due to the absence of the mineral ions that typically give water its characteristic taste. Purified water, particularly that sold for drinking, often undergoes a final step where a minute amount of minerals or electrolytes is intentionally added back, known as re-mineralization. This re-mineralization improves the taste significantly, making the water more palatable for general consumption.
Ideal Applications for Each Water Type
The concept of which water is “better” depends entirely on the intended application, as their unique characteristics suit different needs. Distilled water’s near-total absence of minerals makes it the preferred choice for sensitive mechanical and laboratory applications.
Distilled Water Applications
In household appliances like steam irons, humidifiers, or car batteries, using distilled water prevents the buildup of mineral deposits, known as scale. Scale can damage internal components and reduce efficiency. For scientific experiments and medical use, its mineral neutrality is necessary to avoid interference with precise results.
Purified Water Applications
Purified water is the more practical and common choice for daily drinking and cooking, especially when re-mineralized for a more pleasing flavor. While both types are safe to drink, purified water offers a cleaner taste profile and a more balanced composition for regular hydration. For applications requiring high purity but not absolute mineral neutrality, such as water coolers or food processing, purified water is generally the more cost-effective and readily available option.