Leaving bottled water in your car, especially during warmer months, is a common practice with potential health risks that many people overlook. The intense heat inside a parked car can accelerate chemical processes within the plastic, affecting the water's taste and purity. Understanding the factors at play can help you make safer choices for your health.
The Breakdown of Plastic and Chemical Leaching
Most single-use water bottles are made from polyethylene terephthalate (PET). While generally safe for initial use, high temperatures and prolonged sun exposure can cause PET to break down, leading to the leaching of microscopic fragments and chemical compounds into the water.
Potential compounds that can leach include antimony, a metalloid used in PET production, and Bisphenol A (BPA) from other plastic types used in reusable bottles. Although PET bottles are typically BPA-free, heat can increase the leaching of BPA, which is an endocrine disruptor.
The Hidden Danger of Bacterial Growth
Bacterial contamination is another significant risk. While an unopened bottle in a hot car is relatively safe, opening it introduces bacteria from your mouth. The warm car environment is an ideal place for these bacteria to multiply rapidly.
Tests on opened water bottles left in hot vehicles have shown the presence of coliform bacteria, indicating unsanitary conditions due to the multiplication of bacteria from the drinker's mouth.
How long is too long?
- Short-Term (A few hours): Water may develop a plastic taste or smell, indicating some chemical leaching. While not immediately harmful, it suggests reduced quality.
- Medium-Term (24+ hours): Chemical leaching increases with prolonged heat exposure. If opened, significant bacterial growth is likely. It is generally advised not to drink this water.
- Long-Term (Weeks or months): Plastic degradation and the release of chemicals and microplastics are substantial. Opened bottles also present a high bacterial risk.
Safest Alternatives to Storing Water in Your Car
Safer options for keeping water in your car that avoid the risks associated with heat and plastic include:
- Insulated Stainless Steel Bottles: Excellent for maintaining temperature and preventing leaching, as stainless steel is inert.
- Glass Bottles: A safe, non-porous and inert option, though they are prone to breaking.
- Coolers and Thermal Bags: These insulate bottles from heat and sunlight, slowing down leaching and bacterial growth.
Comparison of Bottle Types for In-Car Storage
| Feature | Single-Use Plastic Bottle | Reusable Plastic Bottle (BPA-Free) | Insulated Stainless Steel Bottle | Glass Bottle |
|---|---|---|---|---|
| Chemical Leaching | High (accelerated by heat and UV) | Low (but can occur over time with heat) | None (inert material) | None (inert material) |
| Bacterial Growth | High risk, especially if opened | Moderate risk (porous plastic can trap bacteria) | Low risk (easy to clean, non-porous) | Low risk (easy to clean, non-porous) |
| Durability | Low (designed for single use) | Moderate (but degrades over time) | High | Low (fragile) |
| Cost | Very Low | Moderate | High | Moderate |
| Environmental Impact | High (single-use waste) | Moderate | Low (long-lasting) | Moderate (can be recycled) |
Conclusion
Leaving bottled water in a hot car, especially for extended periods, carries risks from chemical leaching and bacterial growth. While a short time in moderate heat might not be severely harmful, it's best to avoid the practice. For safe hydration on the go, consider using insulated stainless steel or glass bottles, or storing water in a cooler. Always discard water that has an unusual smell, taste, or appearance.
Best Practices for Vehicle Hydration
Here are some final takeaways for staying safely hydrated while on the go:
- Use a cooler or insulated container to protect water bottles from temperature fluctuations.
- Rotate your bottled water stock regularly and avoid leaving it for more than a day or two in warm weather.
- Never re-use single-use plastic bottles, as the plastic breaks down faster with repeated use and washing.
- Opt for glass or stainless steel reusable bottles, which are durable and do not leach chemicals.
- Park in shaded areas whenever possible to keep your car's interior temperature down.
- Before consuming, inspect the bottle for any signs of physical damage or changes in the water's appearance, smell, or taste.
For more information on the safety of plastic food and beverage containers, a great resource is the U.S. Food and Drug Administration's website.
