The quest for the “purest” drinking water often confuses chemical purity with beneficial consumption. While purity suggests the complete absence of contaminants, this ideal chemical state does not necessarily translate to the healthiest or best-tasting water for the human body. Optimal water for daily drinking involves a complex balance of contaminant removal and mineral content. The definition of what is “best” moves beyond a simple scientific measurement of zero, incorporating factors like taste, biological need, and long-term effects. Understanding the processes that create varying levels of purity is the first step in determining what water is right for an individual’s needs.
Defining Water Purity
The scientific metric used to define water purity is primarily Total Dissolved Solids (TDS). TDS measures the concentration of all inorganic salts, organic matter, and other dissolved particles present in a given volume of water. This concentration is typically quantified in units of parts per million (ppm) or milligrams per liter (mg/L). A lower TDS reading indicates a chemically purer water sample. Regulatory bodies like the U.S. Environmental Protection Agency (EPA) establish guidelines for acceptable TDS levels in public drinking water, often setting an aesthetic objective of less than 500 mg/L. This standard is generally based on taste and the potential for scale buildup, rather than direct health concerns. Beyond TDS, electrical conductivity is used as a secondary indicator, since dissolved ions increase a water’s ability to carry an electric current. A lower conductivity measurement correlates with fewer dissolved solids and higher purity.
The Apex of Purity: Distilled and Deionized Water
The highest levels of chemical purity are achieved through processes that produce distilled and deionized water, often resulting in TDS levels approaching zero.
Distillation
Distillation involves boiling water and then collecting the steam as it condenses back into a liquid. This process effectively leaves behind heavy metals, salts, and non-volatile contaminants.
Deionization (DI)
Deionization water is created using ion-exchange resins that chemically swap positively charged ions with hydrogen ions and negatively charged ions with hydroxyl ions. These ions then recombine to form pure water. This method is highly effective at removing dissolved mineral salts, often achieving an even higher purity than distillation.
These hyper-pure forms of water are not typically intended for long-term daily consumption, but rather for specific technical and medical uses. Distilled water is commonly used in CPAP machines, humidifiers, and laboratory applications where mineral deposits must be avoided. Deionized water’s extreme purity makes it suitable for semiconductor manufacturing, pharmaceutical production, and specialized laboratory testing. The processes that strip water of all dissolved solids make these types of water chemically pure but often unappealing for drinking due to a flat or insipid taste.
Commercial Purification Methods and Their Output
Consumers seeking high-purity water for daily drinking generally encounter purification methods that achieve a significant reduction in contaminants without reaching the near-zero TDS of laboratory-grade water.
Reverse Osmosis (RO)
Reverse Osmosis (RO) is the most widespread consumer method for creating purified drinking water. This process forces water through a semipermeable membrane under pressure, effectively screening out up to 99% of dissolved solids, ions, and large molecules. RO systems typically reduce TDS levels to under 25 ppm, or sometimes as low as 50-150 ppm in optimized consumer systems. The resulting water is substantially cleaner than tap water, which often falls between 50 ppm and 1,000 ppm.
Other Household Methods
Activated carbon filtration primarily works by adsorption, effectively removing substances that affect taste and odor, such as chlorine and certain organic contaminants. Carbon filters have minimal impact on the overall TDS level, as they do not remove inorganic salts or minerals. Ultraviolet (UV) treatment uses UV light to disrupt the DNA of pathogens like bacteria and viruses. This method is highly effective for disinfection, but it is purely a sterilization process and does not alter the chemical composition or the TDS reading of the water.
Purity Versus Health: The Role of Minerals
While chemical purity is defined by the absence of dissolved solids, the healthiest water for human consumption involves a nuanced consideration of mineral content. Water that is hyper-pure, such as distilled or highly-filtered RO water, is considered hypotonic. When this hypotonic water enters the body, it creates an osmotic pressure gradient that can draw essential minerals and electrolytes out of the body’s cells and tissues. Long-term consumption of demineralized water may lead to a loss of beneficial minerals and a disruption of electrolyte balance.
The minerals naturally present in water, particularly calcium and magnesium, are easily absorbed by the gastrointestinal tract and contribute to overall dietary intake. Research suggests health benefits are associated with drinking water containing at least 20–30 mg/L of calcium and 10 mg/L of magnesium. These minerals are important for bone health, muscle function, and nerve signaling.
Therefore, the optimal drinking water represents a balance: low in contaminants to ensure safety, but containing a moderate level of desirable dissolved solids to support bodily functions and provide a palatable taste. Water with a TDS level between 50 and 150 ppm is often cited as the ideal range, offering both high purity and an acceptable mineral presence for taste and health.