What Makes Water Go 'Stale'?
Water doesn't chemically go bad, but its properties and taste can change over time through interaction with its environment. This phenomenon is often referred to as becoming 'stale.' The most common cause is the absorption of atmospheric gases. When water is left uncovered, it absorbs carbon dioxide (CO2) from the air. This CO2 dissolves and forms a weak carbonic acid, which slightly lowers the water's pH level and gives it a slightly different, flatter taste.
Another significant factor for tap water is the evaporation of chlorine. Municipal tap water is treated with chlorine to kill bacteria and viruses. When left uncovered, this chlorine dissipates over time, which can change the flavor and leave the water more susceptible to bacterial growth.
The Safety of Day-Old Water
For most healthy individuals, drinking a glass of water that has been sitting out overnight is unlikely to cause any harm. The bacteria introduced, primarily from your mouth or settling dust, are typically from your own environment and not in a high enough concentration to cause illness. However, this safety assumption changes under certain conditions:
- Sharing: If multiple people drink from the same container, the risk of introducing and spreading different bacteria increases.
- Immunocompromised Individuals: For those with weakened immune systems, even low levels of bacteria can pose a risk, making it safer to use fresh water daily.
- External Contaminants: An uncovered glass is a landing pad for dust, airborne particles, and insects. While often harmless, it's not the most hygienic practice.
- Heat Exposure: Storing water in a hot environment, like a car, can accelerate bacterial growth, making it unsafe to drink.
Risks of Storing Water in Plastic Bottles
While water itself doesn't expire, the plastic container it's in does. The expiration date on bottled water refers to the integrity of the bottle, not the water inside. Over time, especially when exposed to heat or sunlight, chemicals from the plastic, like bisphenol A (BPA) and polyethylene terephthalate (PET), can leach into the water. While the FDA has stated these levels are too small to cause immediate health issues, long-term exposure and effects are still under study, and many people prefer to avoid the risk.
How to Tell if Your Water is Unsafe
If you are unsure whether water is safe to drink, always err on the side of caution and discard it. Key signs that water may be contaminated or unsafe include:
- Cloudiness or Discoloration: A cloudy or off-colored appearance can indicate sediment or bacterial growth.
- Visible Particles: The presence of visible sediment, rust, or other floating particles suggests contamination.
- Strange Odor: Foul, chemical, or rotten-egg smells are strong indicators of potential issues like hydrogen sulfide or other pollutants.
- Off-putting Taste: Besides the normal flat taste, any metallic, salty, or overly chemical taste suggests a problem.
- Oily Film: An oily sheen on the surface can be a sign of excess minerals or contaminants.
Best Practices for Safe Water Storage
To ensure your drinking water remains fresh and safe, proper storage is key.
- Use appropriate containers: Opt for glass, high-grade stainless steel, or BPA-free plastic for storage. Avoid reusing single-use plastic bottles, as they can break down and harbor bacteria.
- Keep it covered: Always use an airtight lid to prevent airborne contaminants like dust and bacteria from entering your water.
- Store in a cool, dark place: Keeping water away from heat and direct sunlight slows down bacterial growth and prevents plastic degradation.
- Sanitize containers regularly: Wash reusable containers daily with soap and water to prevent bacterial buildup.
- Rotate your supply: For emergency water storage, replace the water every six months to ensure it remains as fresh as possible.
Comparison of Water Storage Options
| Feature | Tap Water (Unsealed Glass) | Tap Water (Sealed Container) | Bottled Water (Sealed) | Reusable Bottle (Daily Use) |
|---|---|---|---|---|
| Recommended Lifespan | 12-24 hours | Up to 6 months | Up to 2 years (best-by date) | Consume within a few hours |
| Taste Change Risk | High (due to CO2 absorption) | Low (if airtight) | Moderate (plastic permeability) | Moderate (backwash, temp fluctuation) |
| Bacterial Growth Risk | Moderate (exposed) | Low (if stored clean) | Low (sealed) | High (mouth contamination) |
| Chemical Leaching | None | None (if glass/steel) | Possible (from plastic) | Possible (reusing plastic) |
| Cost | Very Low | Low | Moderate | Moderate to High (Initial) |
Conclusion
While a glass of water left out overnight is generally safe for you to drink, it won't be as fresh as newly poured water due to changes in taste and potential minor contamination. The risks increase with improper storage, prolonged exposure to heat and sunlight, and the use of certain plastics. To ensure the highest quality and safety, always store water in clean, airtight containers made of glass or stainless steel, keep it in a cool, dark place, and consume it within a reasonable timeframe. Paying attention to your senses—if the water looks, smells, or tastes off—is the best way to determine if it's time to pour it out and refill. For more information on safe water storage and handling, refer to the CDC's guidelines.
Disclaimer: This article provides general information and is not a substitute for professional medical or health advice.
