Storing cases of bottled water in a hot garage, shed, or car trunk is a common practice. However, the high temperatures found in these environments—often exceeding 100°F (38°C) during summer months—can compromise the product and the integrity of the plastic packaging. Understanding the interaction between heat, plastic, and water is important for determining if the water remains safe for consumption and maintains its intended quality. This information explores the scientific reasons why this storage method is discouraged and outlines better practices for maintaining a safe water supply.
Chemical Migration and Plastic Degradation
The majority of single-serving bottled water containers are made from Polyethylene Terephthalate, or PET. This material is generally considered stable, but elevated temperatures significantly accelerate the transfer of chemical compounds from the plastic into the water. One primary concern is the migration of antimony, a metalloid compound used as a catalyst in the manufacturing process of PET plastic.
Studies have shown that antimony concentrations in water increase with both the duration of storage and the temperature of the environment. For example, temperatures exceeding 122°F (50°C), which a closed garage can easily reach, cause the rate of antimony release to increase rapidly. At temperatures as high as 158°F (70°C), concentrations of antimony have been found to increase dramatically in a short period. While the levels of these compounds are often within current regulatory limits under normal conditions, prolonged exposure to excessive heat can push them past established safety standards.
The heat-induced movement of molecules within the plastic also facilitates the migration of other substances, including trace amounts of phthalates and, less commonly in new PET bottles, Bisphenol A (BPA). Heat essentially excites the molecules in the plastic, causing them to break down slightly faster and release their constituent parts into the water. This process is a direct result of thermal stress on the polymer structure, and it is the main reason why storing bottled water in a hot garage raises health and quality questions.
Effects of High Heat on Water Quality
Beyond chemical migration, high temperatures directly impact the aesthetic qualities of the water, leading to noticeable changes in taste and odor. The warmth causes the water to absorb volatile organic compounds from the plastic, such as acetaldehyde. Acetaldehyde migration is responsible for the distinct “plastic” or sometimes “fruity” taste that consumers often detect in water that has been sitting in a hot environment.
The plastic bottles are not perfectly sealed against the surrounding environment; they are slightly permeable. If the water is stored near strong-smelling chemicals commonly found in a garage, such as gasoline, paint thinners, or household cleaners, the water can absorb those vapors. Elevated temperatures intensify the concentration and volatility of these external chemicals, making it easier for them to pass through the plastic and affect the water’s taste and smell.
Although purified bottled water is not prone to spoilage like other beverages, sustained high temperatures can create conditions favorable for microbial growth. If the bottle seal was compromised, or if the water was not completely sterile upon bottling, exposure to heat and direct sunlight can infrequently lead to the development of algae or mold. While this is primarily an aesthetic concern and not typically a public health threat in a sealed bottle, the main result of heat exposure is an unpleasant, stale flavor that diminishes the overall quality of the water.
Recommended Safe Storage Practices
To ensure bottled water maintains its quality and minimizes the potential for chemical migration, it should be stored in a cool, dark, and stable environment. The ideal temperature range for storage is generally considered to be between 50°F and 70°F (10°C and 21°C). Storing water in a climate-controlled area, such as a pantry, basement, or utility closet, will prevent the thermal stress that causes plastic degradation.
It is important to keep bottled water away from any household chemicals, cleaning supplies, or fuels that emit strong odors. The slight permeability of the plastic packaging makes it susceptible to absorbing ambient gases, which will taint the water’s taste. Since the water itself does not technically expire, the “best by” date refers to the container’s integrity and the potential for leaching over time.
For long-term storage, the general recommendation is to consume or rotate the supply every six months to two years, prioritizing freshness. If bottled water has been exposed to extreme heat, it is best practice to discard it. This action eliminates the risk of consuming water with elevated levels of leached chemicals and ensures you are not drinking water with an unpleasant, plastic-like taste.