Bottled water is often seen as having an indefinite shelf life due to its sealed container and source protection. While the water molecule itself does not truly “go bad” in the traditional sense of food spoilage, its quality can diminish over time. This perceived spoilage is a consequence of external factors affecting the container or the water after the seal is broken. The safety and pleasantness of bottled water depend heavily on storage conditions and consumption methods, introducing risks that compromise its initial purity. These risks involve both the slow transfer of compounds from the plastic packaging and the rapid introduction of microorganisms from the consumer.
Chemical Migration: When Plastic Affects Water Quality
The primary material used for single-serving water bottles is polyethylene terephthalate (PET), which the Food and Drug Administration (FDA) approves for food and beverage contact. PET plastic can release trace amounts of chemical compounds into the water, a process known as migration. The rate and quantity of this migration are highly dependent on environmental conditions, particularly temperature and the duration of storage.
Heat is the most significant factor that accelerates this transfer of substances from the plastic into the liquid inside. Storing bottles in hot environments, such as a sun-drenched car or a non-air-conditioned warehouse, increases the kinetic energy within the plastic structure. This elevated energy state allows compounds like antimony, a catalyst used in PET production, and trace amounts of acetaldehyde to move more readily into the water.
Acetaldehyde is a compound that can migrate from the plastic and is primarily responsible for an altered taste or odor, often described as sweet or fruity. Although the levels of these migrating chemicals generally remain well below regulatory safety limits, extended periods of storage, especially at temperatures above 104°F (40°C) to 122°F (50°C), can significantly increase their concentration. This phenomenon compromises the water’s quality.
Microbial Growth After Opening
Once a bottle’s factory seal is broken, the water’s purity shifts from a controlled environment to one susceptible to biological contamination. Issues with opened bottled water stem directly from the introduction of microorganisms from the person drinking it. The act of drinking directly from the bottle transfers oral bacteria into the water, where they can rapidly begin to multiply.
Studies show that after a single person drinks from a bottle, the bacterial count can increase dramatically within 48 hours, especially when stored at room temperature or warmer. The bacteria introduced are generally non-pathogenic, originating from the normal human oral flora, such as species of Streptococcus and Staphylococcus. The moist, nutrient-poor environment, combined with a warm temperature, creates a suitable incubator for microbial growth.
The plastic container itself does not foster this growth; rather, it is the vessel that holds the contaminated water. While sealed bottled water undergoes rigorous testing to ensure it is free from indicator bacteria like E. coli, once opened, the consumer becomes the primary source of biological compromise. This rapid microbial proliferation is why opened bottled water is considered less safe than its freshly sealed counterpart.
Best Practices for Bottled Water Storage
Maintaining the original quality of bottled water relies heavily on proper storage before and after the seal is broken. To prevent the migration of chemical compounds and maintain taste, store all unopened bottles in a cool, dark location. Keeping the water away from direct sunlight or extreme heat, such as garages or hot vehicles, helps ensure the integrity of the PET plastic.
Plastic is slightly permeable, meaning it can absorb airborne chemicals and odors. Bottles should be stored away from strong-smelling household cleaners, gasoline, or paint thinners to prevent volatile organic compounds from permeating the plastic and affecting the water’s taste. This separation ensures that the water retains its neutral flavor.
Once the bottle is opened, consumption should occur quickly to minimize bacterial proliferation. It is advised to consume opened bottled water within one to two days if kept at room temperature. For single-use plastic bottles, avoid refilling them, as the plastic is not designed to withstand repeated cleaning, and wear and tear can create micro-fissures that harbor bacteria.