The Science of Water "Going Bad"
Water itself, as a chemical compound (H2O), does not spoil in the traditional sense like food. However, once it comes into contact with the environment or a container, its quality, taste, and safety can degrade. This degradation is often referred to as water "going bad." Several key factors contribute to this process:
- Bacterial Contamination: The most significant risk comes from bacteria. Every time you take a sip from a bottle or glass, you introduce bacteria from your mouth. These microbes can multiply rapidly, especially in a warm environment. Even a clean, open glass is vulnerable to airborne particles and microbes. Reusable water bottles, if not cleaned daily, are particularly prone to developing biofilms—a slimy layer of microorganisms.
- Chlorine Dissipation: Tap water is treated with chlorine to kill bacteria and other pathogens. When water sits out, this chlorine dissipates into the air, removing its built-in defense against bacterial growth. This process can be accelerated by heat and exposure to sunlight.
- Absorption of Gases and Odors: Water is a universal solvent and will absorb gases and odors from its surroundings. When left uncovered, it absorbs carbon dioxide from the air, which lowers its pH slightly and gives it a stale or flat taste. Storing water near pungent items, like onions or cleaners, can also transfer odors and flavors through permeable containers, especially plastic.
- Chemical Leaching from Containers: For bottled water, the risk comes from the container itself. Plastics, especially single-use ones made of Polyethylene Terephthalate (PET), can degrade over time and leach chemicals, like BPA, into the water. This process is significantly accelerated by heat, which is why drinking bottled water left in a hot car is highly discouraged.
Proper Storage for Safe, Fresh Water
To ensure your drinking water stays fresh and safe, proper storage is crucial. The following practices can help minimize the risk of contamination and maintain quality over time.
Best Practices for Everyday Use
- Keep it covered: Always use a water bottle with a secure lid or keep a lid on a pitcher. This simple step prevents airborne dust and contaminants from entering.
- Wash reusable bottles daily: For reusable bottles, daily cleaning with hot, soapy water is essential to prevent bacterial growth and biofilms.
- Choose the right container: Glass or high-quality stainless steel are the best choices for taste and safety, as they are non-porous and won't leach chemicals.
- Avoid extreme temperatures: Store water in a cool, dark place away from direct sunlight or heat sources. Heat accelerates bacterial growth and chemical leaching from plastics.
- Rotate your supply: For long-term storage, rotate your water supply every six months to ensure optimal freshness.
Comparison of Water Types for Storage
| Water Type | Recommended Storage Duration | Key Considerations |
|---|---|---|
| Tap Water (Uncovered) | 12–24 hours | Chlorine dissipates, allowing bacteria to grow. Absorbs ambient odors. |
| Tap Water (Sealed) | Up to 6 months | Chlorine keeps bacteria at bay initially. Should be stored in a cool, dark place to maintain freshness. |
| Filtered Water | A few hours (room temp) | Chlorine-free, so bacteria can grow quickly. Best stored sealed and refrigerated for 3–5 days. |
| Bottled Water (Unopened) | 1–2 years (per "best by" date) | Expiration refers to plastic degradation, not the water itself. Store in a cool, dark place. |
| Bottled Water (Opened) | 12–24 hours (room temp) | Oral bacteria introduced upon sipping. Refrigerate and consume within a few days for safety. |
| Distilled Water (Unopened) | Indefinitely | Stored in non-leaching, sealed containers, it's very stable. Container material is the main concern. |
When to Discard Old Water
It's always best to be cautious when in doubt. Here are some signs that indicate it's time to pour out the old water and get a fresh glass:
- Cloudiness or Discoloration: Visible changes to the water's clarity can indicate microbial growth or chemical reactions.
- Off-Putting Odors: If the water smells musty, foul, or chemical-like, it has likely been contaminated. Mold can grow on the inside of bottle caps, creating a distinct smell.
- Unpleasant Taste: An acidic, stale, or metallic taste is a clear signal that the water is no longer fresh.
- Long-Term Exposure: Any water left open for more than a day, or sipped from and left for multiple days, poses an increased risk of bacterial contamination.
Conclusion
While pure water cannot inherently "go bad," leaving it out and unrefrigerated creates conditions where taste can degrade and contaminants can be introduced. The biggest threats are bacterial growth from contact and chemical leaching from plastic containers, especially when exposed to heat. By using clean, sealed, food-grade containers, keeping water in a cool, dark place, and consuming it within a day or two of being opened or left out, you can ensure your water remains safe and fresh. For emergency storage, specific guidelines from health organizations like the CDC should be followed. Ultimately, for everyday hydration, fresh is always best. For more in-depth information on emergency water supplies, visit the CDC's guide.
