Water purification removes unwanted substances to produce cleaner, safer water. While both distilled and filtered water achieve this goal, they are fundamentally different products created through distinct methods. The core difference lies in the purification principles used, which determines the final composition and the applications for which each type is best suited.
How Distilled Water and Filtered Water Are Made
Distilled water is created through a thermal process that mimics the natural water cycle. This method involves heating water to its boiling point, converting it into steam and leaving behind virtually all non-volatile impurities such as minerals, heavy metals, and salts. The purified steam is then collected, cooled, and condensed back into liquid water, resulting in a product that is nearly 100% pure H2O.
Filtered water, by contrast, relies on physical or chemical barriers to remove contaminants. The process involves pushing water through various media, where impurities are either physically blocked or chemically captured. Common filtration systems range from simple activated carbon filters to complex multi-stage systems like reverse osmosis (RO).
Reverse osmosis (RO) employs applied pressure to force water through a semi-permeable membrane, which acts as an extremely fine screen. This membrane blocks molecules larger than water, effectively separating a wide array of dissolved solids from the clean water stream. The purification level of filtered water is highly dependent on the type and quality of the filtration media used.
Key Differences in Water Composition
The compositional difference is quantified by measuring the Total Dissolved Solids (TDS), which represents the concentration of all inorganic and organic substances dissolved in the water. Distillation is the most effective method for reducing TDS, producing water with a concentration often measured at 1 to 5 parts per million (ppm). This extreme purity is achieved because the boiling and condensation process leaves nearly every non-water substance behind.
Filtered water maintains a measurable, though significantly reduced, TDS level depending on the system employed. A standard carbon filter, commonly found in pitchers, primarily targets taste and odor by removing chlorine, but it only reduces TDS by about 10–15%. Reverse osmosis filtration is far more rigorous, typically removing between 93% and 99% of dissolved solids, which can result in a TDS range of 5 to 50 ppm.
The type of contaminants removed highlights the differences in the purification mechanisms. Distilled water removes virtually all non-volatile inorganic substances, including heavy metals, salts, and minerals, and kills microorganisms through high-temperature steam. Filtered water, especially through RO, is excellent at removing specific contaminants like lead, fluoride, and sediments, but it retains some trace minerals unless further polishing is used.
The presence or absence of natural minerals like calcium and magnesium is a defining characteristic. Distillation strips the water of these minerals entirely, yielding demineralized water. Most filtered water systems, particularly standard carbon filters, allow a beneficial concentration of these compounds to remain, which often improves the taste profile.
Choosing the Right Water for Specific Needs
The intended use dictates whether distilled or filtered water is the appropriate choice. Distilled water is preferred for applications where the prevention of mineral buildup is necessary, due to its near-zero TDS level. This makes it the standard for use in:
- Laboratory procedures.
- Medical devices like CPAP machines.
- Steam irons.
- Car batteries.
Using water with measurable dissolved solids in these appliances can lead to scale formation, which impairs function and shortens the device’s lifespan.
Filtered water is the favored option for daily consumption, including drinking and cooking. Filtration systems, especially those incorporating activated carbon, remove compounds that cause unpleasant tastes and odors, such as chlorine, while retaining beneficial minerals. This retention contributes to a more natural and palatable flavor compared to the flat taste associated with demineralized water.