Storing water in plastic bottles is common for daily hydration or emergency preparation. While water itself is stable and does not chemically expire, the container imposes a limit on storage duration. Understanding this limit requires examining the plastic itself and the environmental factors that affect it. This analysis explains how long water can be safely stored in plastic containers.
Recommended Shelf Life for Commercial Water
The U.S. Food and Drug Administration (FDA) does not legally require an expiration date on commercially bottled water, as properly packaged water has an indefinite safety shelf life. Despite this, most companies print an expiration date, typically one to two years from bottling. This date measures the container’s quality and potential aesthetic changes, not water safety. For emergency preparedness, organizations like the CDC and FEMA recommend storing a water supply. If commercially bottled water is stored under ideal conditions, it can last for extended periods.
Material Degradation and Chemical Leaching
The time limit on water stored in plastic bottles is due to the physical breakdown and chemical release from the container material. Most single-use bottles are made from polyethylene terephthalate (PET), a polymer that degrades over time and under stress. Heat and sunlight accelerate this degradation, weakening the plastic structure’s chemical bonds. As the polymer breaks down, it releases compounds into the water, a process known as chemical leaching. For example, antimony, a metalloid used as a catalyst in PET production, increases in concentration the longer water sits in the bottle, and leaching rates for chemicals like phthalates and bisphenols rise significantly when bottles are exposed to temperatures above 95°F (35°C).
Factors Affecting Water Quality Over Time
External factors related to the storage environment can compromise water quality over time, beyond internal chemical changes from the plastic. Commercially sealed bottles are not completely sterile and can harbor low levels of heterotrophic bacteria. Higher temperatures encourage the growth of these microbes, potentially increasing bacterial populations. Plastic containers are also characterized by gas permeability, allowing small molecules from the surrounding air to pass through the walls. This permeability allows atmospheric gases like oxygen and carbon dioxide to enter, subtly altering the taste, and also risks contamination from strong odors or vapors from nearby household chemicals.
Maximizing Safe Water Storage Duration
Controlling environmental conditions is paramount to extending the safe storage life of bottled water. Storing plastic bottles in a cool environment, ideally below 70°F (21°C), significantly slows the rate of plastic degradation and chemical leaching. A dark storage location is also beneficial because ultraviolet (UV) light accelerates the breakdown of the plastic polymer, encouraging chemical migration. Keep water bottles elevated and away from concrete floors, as the porous material can sometimes leach chemicals that the plastic may absorb. Finally, to mitigate the risk of taste and odor contamination due to permeability, always store water supplies away from strong-smelling substances like paints, fuels, or solvents.