The desire for “pure water” often stems from the belief that removing all traces of other substances makes it inherently healthier. This pursuit frequently confuses scientific purity with optimal health benefits. Water purity is a measurable, scientific concept defined by the absence of dissolved solids and contaminants. This article explores the technical definition of water purity, compares the levels achieved by various methods, and examines the physiological implications of consuming water at its most refined state.
Defining Water Purity
The most common and measurable indicator of water purity is the level of Total Dissolved Solids (TDS). TDS represents the combined concentration of all inorganic and organic substances present in the water, including minerals, salts, and organic matter. It is measured in parts per million (ppm) or milligrams per liter (mg/L). Lower TDS levels signify higher water purity because fewer extraneous materials remain suspended.
While TDS is a comprehensive measure of purity, it does not distinguish between potentially harmful substances and beneficial ones, such as calcium and magnesium. Purity measures also seek to eliminate biological contaminants like microbes and chemical pollutants like heavy metals and pesticides. For context, water with TDS levels below 50 ppm is considered pure, while typical tap water often falls between 50 and 500 ppm.
Types of Highly Purified Water
The purest forms of water, often achieving near-zero TDS, are typically created for industrial, laboratory, or medical applications rather than regular drinking. Distillation and deionization achieve the highest levels of purity. These processes are designed to strip the water of virtually all inorganic solids and ions.
Distillation involves boiling the water and then collecting the resulting steam as it condenses back into a liquid. Since most dissolved solids and minerals do not vaporize, they are left behind. This produces water with a TDS level that can be less than 10 ppm. This process is effective but can be energy-intensive and slow.
Deionization (DI) water achieves high purity by passing water through ion-exchange resins. These resins swap positively charged ions (cations) for hydrogen ions and negatively charged ions (anions) for hydroxyl ions. The hydrogen and hydroxyl ions then combine to form pure H₂O, resulting in water that can reach a TDS level of 0 ppm. DI water is used in laboratories and manufacturing where the absence of ions is required to prevent interference with chemical reactions or delicate components.
Commercial Drinking Water Purity Comparison
The average consumer encounters several types of commercially available or home-filtered water, each with a distinct purity profile. Reverse Osmosis (RO) water offers the highest level of purification among commonly available consumer methods. The RO process forces water through a semi-permeable membrane that blocks most dissolved solids and contaminants.
A high-quality RO system can reduce TDS levels to a range of 10 to 50 ppm, making it a highly pure drinking option, though not as pure as laboratory-grade distilled water. RO is a popular choice for treating water with high initial TDS levels, often exceeding 300 ppm.
In contrast, bottled spring and mineral waters are defined by their source and mineral content, meaning they are intentionally not the purest by the TDS metric. Mineral water must contain at least 250 ppm of TDS to be labeled as such, with many popular brands having levels between 340 and 854 ppm. These dissolved solids, primarily beneficial minerals like calcium and magnesium, contribute to the water’s characteristic taste.
Standard carbon filtration, often found in pitcher filters or refrigerator systems, operates differently and does not significantly reduce overall TDS. Carbon filters work by adsorption, effectively removing taste and odor contaminants like chlorine. While they improve the water’s aesthetic quality, they are the least pure processed option because they leave the majority of inorganic dissolved solids in the water.
Health Considerations of Extreme Purity
The physiological effects reveal that the “purest” water is not necessarily the healthiest choice for long-term consumption. Water subjected to extreme purification, such as distillation or deionization, is virtually devoid of minerals. This de-mineralized state can have negative consequences on the body’s internal balance over time.
Naturally occurring minerals like calcium and magnesium are beneficial, and water can contribute to the daily intake of these elements. Consuming water with low TDS levels can lead to a diuretic effect, increasing urine output and disturbing the body’s electrolyte balance. Studies indicate that using de-mineralized water for cooking can cause a loss of essential elements from foods, sometimes reducing the calcium and magnesium content by over 60%.
The body’s intestinal lining must first add electrolytes to highly pure water before absorption, effectively pulling minerals from the body’s reserves to achieve balance. Long-term consumption of water lacking minerals has been associated with various health concerns, including a higher risk of cardiovascular diseases due to the absence of magnesium and calcium. Optimal drinking water involves a balance where purification removes harmful contaminants while retaining a sufficient level of beneficial dissolved solids. A TDS level between 50 and 150 ppm is often recommended for taste and health.