Bottled water is generally considered safe for human consumption, but it is not sterile. The term “sterile” applies to a rigorous medical or laboratory standard, which is far stricter than what is necessary for drinking water. Bottled water is a highly regulated food product designed to meet strict governmental standards for public health. Bottlers focus on eliminating harmful pathogens and significantly reducing the overall microbial load, not on the complete removal of every single microorganism.
Defining “Sterile” vs. Safe to Drink
The word “sterile” means the complete absence of all living microorganisms, including bacteria, fungi, viruses, and spores. Achieving this purity requires extreme measures like high-temperature autoclaving or intense radiation, often meeting U.S. Pharmacopeia standards for medical applications. Sterile water is intended for uses such as wound irrigation or preparing infant formula.
In contrast, “safe to drink” water meets government standards ensuring it is free from disease-causing agents and harmful chemicals. Bottled water must comply with Food and Drug Administration (FDA) regulations focused on eliminating public health risks. This standard allows for trace amounts of non-pathogenic, naturally occurring bacteria, which prevents bottled water from being technically sterile.
Water Sources and Purification Methods
Bottled water originates from protected natural sources, such such as naturally flowing spring water or artesian well water tapped from a confined aquifer. Other products are purified water, often sourced from a public water system, which is then subjected to additional rigorous treatment.
The treatment methods used achieve a high degree of purity and safety, but not sterility. Common purification processes include distillation, which vaporizes and recondenses water to leave impurities behind, and reverse osmosis, which forces water through a semipermeable membrane to remove dissolved solids. Filtration, often using an absolute 1-micron filter, is also used to physically remove protozoa like Cryptosporidium.
A final disinfection step is typically performed just before bottling, often using ozonation or ultraviolet (UV) light. Ozone is a strong antimicrobial agent that effectively kills bacteria and viruses without leaving a residual chemical taste. These methods are highly effective at eliminating pathogens but do not achieve the complete microbial eradication required for a sterility claim.
Microbial Presence and Regulatory Limits
Even after advanced purification, bottled water may contain a small number of harmless, naturally occurring bacteria. These organisms are measured using the Heterotrophic Plate Count (HPC) method, which estimates the total number of live background bacteria. The presence of these HPC organisms is why bottled water is not sterile, though they pose no health risk to the general public.
The FDA regulates bottled water under specific standards, including the microbiological quality requirements outlined in 21 CFR Part 165. Regulations strictly require the water to be free of pathogens, such as E. coli, which would deem the product adulterated. The standards also limit total coliform organisms to no more than one per 100 milliliters of water.
The FDA and the Environmental Protection Agency have determined that naturally occurring HPC organisms pose no public health risk when coliforms are absent. Therefore, neither agency sets a maximum limit for HPCs. Instead, HPC testing serves as a quality control tool for bottlers, monitoring the efficiency of disinfection processes and the cleanliness of equipment.
Factors Affecting Water Purity After Bottling
The quality of bottled water can change significantly after it leaves the manufacturing facility. Immediately after bottling, residual bacteria (HPC) can begin to multiply as the disinfectant, like ozone, naturally dissipates over time. This natural bacterial growth usually involves non-pathogenic organisms like Pseudomonas.
Storage conditions significantly impact the water’s purity and quality. Exposing plastic bottles to high temperatures or direct sunlight accelerates bacterial growth. Heat can also cause the plastic packaging to leach trace amounts of chemical compounds, such as phthalates, into the water, degrading the quality over time. Once the seal is broken, the water becomes susceptible to contamination from the environment, including the air and the user’s mouth.