Water is rarely found in its chemically pure form, naturally containing various dissolved substances and particulates. To improve quality, two common methods are used to remove these impurities: distillation and filtration. While both processes result in cleaner water, they operate on fundamentally different scientific principles. Understanding the difference between distilled and filtered water involves examining the physical mechanisms each uses. This comparison is essential for determining which type of water is appropriate for specific home, health, or mechanical uses.
How Distillation Purifies Water
Distillation is a purification method that mimics the natural hydrological cycle, relying on a change in the water’s physical state. The process begins by heating the source water to its boiling point of \(\text{212}^{\circ}\text{F}\) (\(\text{100}^{\circ}\text{C}\)), converting the liquid into steam. This vaporization step is the mechanism for separating the water from virtually all dissolved contaminants.
The majority of dissolved solids, including minerals, salts, heavy metals, and many microorganisms, cannot vaporize at the same temperature as water and are left behind in the boiling chamber. The resulting pure water vapor is then directed into a separate cooling chamber where it condenses back into liquid water. The collected water is nearly 100% \(\text{H}_2\text{O}\).
Because this process effectively strips the water of everything that does not vaporize, the final product has a Total Dissolved Solids (TDS) measurement of practically zero parts-per-million (PPM). This high level of purity makes it valuable for applications where the absence of any trace element is paramount. Distillation is highly effective at removing non-volatile substances like inorganic minerals, though it may not fully eliminate volatile organic compounds that vaporize along with the water.
The Selective Process of Water Filtration
Water filtration, in contrast to distillation’s phase change, is a physical or chemical process that treats water while it remains in its liquid state. Filtration systems employ various barriers and media to trap or chemically alter contaminants as the water passes through. These systems often utilize multiple stages, such as sediment filters to remove large particles and activated carbon to adsorb chemicals.
Activated carbon filters are commonly used to reduce chlorine, volatile organic compounds, and other substances that can cause unpleasant tastes and odors. The large internal surface area of the carbon chemically attracts and binds these impurities in a process called adsorption. More advanced filtration, such as reverse osmosis (RO), uses pressure to force water through a semipermeable membrane, which physically blocks smaller dissolved inorganic solids like salts.
Filtration is a selective process, meaning the final water content depends heavily on the type and quality of the filter used. Many common household filters are specifically designed to remove harmful contaminants like lead and chlorine while retaining beneficial, naturally occurring minerals such as calcium and magnesium. This selective retention means filtered water is cleaned but not necessarily stripped entirely of its dissolved content, unlike distilled water.
Key Differences in Water Content and Purity
The fundamental difference between the two methods lies in what remains in the water after purification. Distilled water is characterized by its near-zero Total Dissolved Solids (TDS) count, often registering at 1 PPM or less. This near-total absence of minerals and other dissolved matter is the definition of its extreme chemical purity.
Filtered water, while significantly cleaner than tap water, retains a variable TDS level based on the method used. Water labeled as purified, a category which includes some filtered water, must have a TDS of 10 PPM or less. Less intensive filtration methods leave behind beneficial trace minerals, which can result in a TDS that is much higher, often contributing to a more familiar or desirable taste.
The lack of dissolved minerals gives distilled water a distinctively flat or bland taste, which some people find unappealing for drinking. The presence of retained minerals in filtered water acts as a buffer, helping to stabilize the \(\text{pH}\) and improve the water’s flavor profile. The choice between the two often involves balancing ultra-high purity against taste and mineral content.
Choosing the Right Water for Specific Uses
The choice between distilled and filtered water is determined by the intended use. Filtered water is the preferred option for daily consumption, cooking, and making beverages due to its better taste and the retention of healthy electrolytes. It effectively reduces contaminants that affect health and flavor while remaining convenient for general household use.
Distilled water, with its mineral-free composition, is specifically required for applications where mineral buildup, known as scale, must be avoided entirely. This includes sensitive machinery like CPAP machines, clothing irons, and room humidifiers. Using filtered water in these appliances can lead to mineral deposits that damage internal components and affect performance over time.
It is also the standard for many laboratory procedures, medical equipment sterilization, and specific chemical mixing, where even trace minerals could interfere with results. For most people, filtration provides safe, good-tasting water, while distillation serves a precise, technical function.