When consumers read the label “purified water,” a common question arises regarding the chlorine used in municipal water systems. The term “purified” implies the application of advanced processing methods designed to strip the water of virtually all contaminants. This comprehensive treatment is necessary to meet stringent purity standards, and the removal of disinfection chemicals like chlorine and chloramine is a mandatory step. The purification process ensures the final product is a highly processed form of water, free from the chemicals used to disinfect the original source.
The Standard Definition of Purified Water
The designation of “purified water” in the bottled water industry is defined by regulatory benchmarks. To qualify for this label, water must undergo processing that reduces its level of impurities to an extremely low concentration. This purity is quantitatively measured by the Total Dissolved Solids (TDS) content, which includes inorganic salts, organic matter, and various chemicals.
To meet the widely accepted purity standard, the water must contain no more than 10 parts per million (ppm) of TDS. Since chlorine and its byproducts are dissolved chemical compounds, they contribute to the overall TDS measurement. Therefore, any product labeled as purified must necessarily have these disinfection agents removed to fall beneath the strict 10 ppm threshold. This extensive processing ensures that the water meets the United States Pharmacopeia definition of purified water, a standard adopted by the Food and Drug Administration (FDA).
Essential Dechlorination Techniques
Achieving the near-zero contaminant level required for purified water relies on a combination of sophisticated treatment technologies, each targeting different types of impurities. Activated carbon filtration is the first line of defense and the most common method used to remove chlorine and chloramines. The carbon material contains millions of tiny pores that chemically adsorb the chlorine molecules as the water passes through the filter bed. This process effectively neutralizes the chemical disinfectants, which would otherwise interfere with subsequent purification stages.
Reverse osmosis (RO) is another major component of the purification train, involving forcing water through a semi-permeable membrane at high pressure. While the primary function of RO is to remove dissolved inorganic solids, its pores are fine enough to block most chemical contaminants, including residual chlorine compounds.
Distillation further contributes to dechlorination by changing the state of the water from liquid to vapor and back again. When the water is boiled, volatile chemicals like chlorine gas naturally escape, and the purified steam is then collected, leaving non-volatile contaminants behind. Manufacturers often employ a blend of these methods, starting with carbon filtration to protect the sensitive RO membranes, ensuring the complete removal of both free chlorine and the more stable chloramines.
Purified Water vs. Other Common Water Types
The dechlorination required for purified water contrasts sharply with the state of most municipal tap water, which contains chlorine by design. Tap water is intentionally treated with chlorine or chloramines to maintain a residual disinfectant level as it travels through the distribution system to protect public health. The presence of these chemicals is why tap water often possesses a distinct taste or odor.
Simple filtered water, such as that produced by common pitcher filters, typically uses a carbon block to reduce chlorine for taste improvement. However, this level of filtration does not meet the TDS standards of purified water, meaning some contaminants and varying levels of chlorine byproducts may remain.
Spring water, sourced from a natural underground formation, is often naturally low in contaminants but may still be treated with ozone or light chlorination during the bottling process to ensure safety. Unlike purified water, spring water retains its natural mineral content, which results in a high TDS count, meaning it has not been processed to the same degree of purity or mandatory dechlorination.