Bottled water is a common item for hydration, yet the date stamped on the container often causes confusion for consumers. This date suggests the product has a finite shelf life, leading many to question the safety of drinking water that has seemingly expired. To understand the true safety assessment, the focus must shift from the water itself to the packaging that holds it. This article clarifies the reasons behind the printed date and explains the primary safety considerations related to the plastic container.
The Truth About Water Expiration
Pure water (H₂O) does not technically expire or spoil on its own. Unlike perishable foods, water lacks the sugars or proteins necessary for microbial growth or degradation. If sealed in a container and protected from outside contaminants, it can remain chemically stable indefinitely.
The presence of a “best by” or expiration date is primarily due to regulatory requirements for consumable food products. Many state or federal guidelines mandate a printed date on bottled water for traceability and inventory management. Manufacturers often use the same equipment for water, sodas, and juices, making it efficient to apply a date to all products.
While the water remains safe to drink long past this date, prolonged storage can lead to aesthetic issues. Water is an effective solvent and can absorb slight odors or taste compounds from the surrounding air or the plastic itself, resulting in a “stale” or less fresh flavor. This quality degradation, rather than a safety concern, is generally what the date addresses to manage consumer expectations.
The Primary Safety Concern: Chemical Leaching
The actual safety risk associated with older bottled water relates entirely to the container, typically made from Polyethylene Terephthalate (PET) plastic. Over time, the plastic’s chemical structure can degrade, causing its constituent compounds to migrate into the water, a process known as leaching. This migration is significantly accelerated by heat and light exposure, which act as catalysts for the breakdown of the polymer material.
One of the most studied compounds is Antimony, a metalloid used as a catalyst in PET plastic manufacturing. While initial concentrations are very low, studies show that storing bottled water at elevated temperatures dramatically increases the Antimony concentration. For instance, temperatures of 65°C, common inside a car on a hot day, can cause Antimony concentration to exceed the US Environmental Protection Agency’s maximum contaminant level (MCL) of 6 parts per billion (ppb) in just over a month.
Other compounds, such as phthalates and microplastic particles, also become a concern as the plastic breaks down. Phthalates are plasticizers that can migrate into the liquid, and their presence is associated with poor storage conditions. Increased concentrations of these chemicals, particularly after prolonged exposure to high heat, are the main reason safety professionals urge caution with older bottled water.
Minimizing Risk Through Proper Storage
Consumers can effectively mitigate the risks of chemical leaching by focusing on proper storage conditions, which extends the safety window far beyond the printed date. The most effective action is to store bottled water in a consistently cool and dark environment. Temperatures should be kept stable and low, as heat is the primary driver of PET degradation and chemical migration.
It is important to keep bottles away from direct sunlight and other sources of heat, such as garages, enclosed storage units, or the interior of a car. These environments can rapidly reach temperatures that accelerate the release of compounds like Antimony into the water. Storing water in a cool pantry or basement is generally the best practice for long-term safety and quality.
Because PET plastic is slightly permeable, the water can absorb external vapors and odors over time. Therefore, bottled water should be stored away from household chemicals, gasoline, paint, or cleaning products. Controlling temperature, light, and proximity to chemicals ensures the integrity of the plastic container is maintained, keeping the water safe and fresh for an extended period.