Purified water is water that has been processed to remove impurities and contaminants, including chemicals, bacteria, and dissolved solids. It typically starts as tap water or groundwater and undergoes extensive treatment to achieve a very high standard of cleanliness. While purified water is extremely clean and free from potential pollutants, this process removes almost everything else, raising questions about whether the lack of natural mineral content is detrimental to long-term health.
How Water Becomes Purified
The designation “purified water” means the product has been treated to remove virtually all Total Dissolved Solids (TDS), which are inorganic salts and small amounts of organic matter suspended in water. The U.S. Pharmacopeia standard requires a TDS level no greater than 10 parts per million (ppm), which is far lower than the maximum 500 ppm allowed for tap water by the Environmental Protection Agency. This high level of purity is typically achieved through one or a combination of processes.
Reverse Osmosis (RO) is one common method, which forces water under pressure through a semi-permeable membrane. This membrane effectively filters out microscopic particles, dissolved salts, viruses, and bacteria, removing 90 to 99 percent of contaminants. Distillation is another technique where water is boiled into steam, leaving contaminants, minerals, and solids behind, and then the steam is condensed back into liquid form.
Deionization (DI) is a process that specifically removes mineral ions, such as calcium, sodium, and chloride, by exchanging them for hydrogen and hydroxyl ions using specialized ion-exchange resins. While RO and distillation remove a broad spectrum of impurities, DI targets the electrically charged mineral content. These purification methods, often used in sequence, are highly effective at addressing safety concerns related to harmful pollutants.
The Question of Essential Minerals
The primary debate regarding the consumption of purified water centers on its lack of naturally occurring minerals, specifically calcium and magnesium. Water that has undergone aggressive purification methods like distillation or reverse osmosis is often referred to as “demineralized water” due to its extremely low TDS level. While drinking water is not the body’s primary source of these nutrients, the minerals present do contribute to overall daily intake.
The World Health Organization (WHO) has reviewed the health effects of consuming water with very low mineral content over the long term. Studies suggest that water with low levels of calcium and magnesium may be associated with a higher risk of cardiovascular disease mortality. Furthermore, consuming demineralized water may lead to a mild electrolyte imbalance because the intestines must pull electrolytes from the body’s reserves to maintain osmotic balance, resulting in increased elimination of sodium, potassium, and other ions.
The WHO recommends that drinking water should have a minimum Total Dissolved Solids concentration of 100 milligrams per liter (mg/L) and an optimal range between 200 and 400 mg/L. They also suggest minimum concentrations for specific minerals, such as 20 mg/L for calcium and 10 mg/L for magnesium. Because of these concerns, commercial purified water products are sometimes remineralized by adding back a blend of salts to improve taste and address potential health implications. For the average person with a balanced diet, occasional consumption is unlikely to cause immediate harm, but relying on it exclusively long-term is generally not recommended without proper remineralization.
When Purified Water is Recommended
Purified water is often specifically required for applications where the presence of even trace minerals or contaminants could cause problems. For instance, in laboratory and medical settings, highly purified water is essential to prevent interference with sensitive experiments, analytical testing, or equipment function. The use of demineralized water in industrial or technical applications also prevents scaling, which is the mineral buildup that occurs when hard water evaporates.
In a home context, using purified water is beneficial for appliances like humidifiers, CPAP machines, and steam irons. The absence of dissolved solids prevents the formation of mineral scale on heating elements and nebulizers, which prolongs the life of the machine and maintains efficiency. Purified water may also be a temporary choice for individuals with compromised immune systems or those concerned about specific contaminants, such as lead or nitrates, in their local water supply.
For the average healthy person, tap water that meets regulatory standards is considered sufficient and safe for daily consumption. Unless a specific health concern or local water quality issue dictates otherwise, mineralized water sources like tap or spring water are often preferred. Purified water is safe from harmful pollutants, but its primary role in daily life is typically for technical purposes or as a choice for taste, rather than a necessary health upgrade over regulated tap water.