Understanding the Risks of Stagnant Water
Water itself doesn't expire, but the conditions in which it's stored and the container it's in can make it unsafe over time. A glass of water left uncovered on a counter or an open reusable bottle is not a sterile environment. Within days, and certainly after 15 days, it can become a breeding ground for microorganisms and absorb substances from its surroundings.
The Growth of Bacteria and Biofilms
Once you take a sip from a bottle or glass, you introduce bacteria from your mouth into the water. This can cause no harm immediately, but if left to sit for a week or two, these bacteria multiply. Warm temperatures, like those inside a car, can accelerate this growth. These microbes can attach to the container's surfaces and form a slimy, sticky layer known as a biofilm. The Centers for Disease Control and Prevention (CDC) notes that these bacteria can contaminate the water and potentially make you ill. Common health issues from ingesting such microorganisms range from minor stomach upset to more severe waterborne illnesses.
Chemical Leaching from Plastic
Another significant concern with old water, particularly if stored in plastic bottles, is chemical leaching. Disposable PET (polyethylene terephthalate) bottles are designed for single use. Over time, and especially when exposed to heat or sunlight, they can release chemicals like antimony and other endocrine disruptors into the water. While BPA has been phased out of many plastics, other potentially harmful chemicals may still be present. The extended period of 15 days dramatically increases the risk of these compounds accumulating in your water.
Airborne Contaminants and Taste Alteration
If water is left in an uncovered glass for 15 days, it is exposed to everything floating in the air. Dust, dirt, and other small particles can settle on the surface. Furthermore, water is a universal solvent and can absorb odors and flavors from nearby sources. A glass left near the kitchen trash or cleaning products can take on an unpleasant taste and potentially absorb harmful chemicals. The slight staleness you notice in day-old water becomes much more pronounced and unappetizing after 15 days.
Container Material Comparison for Storing Water
| Feature | Reusable Plastic Bottle | Glass Container | Stainless Steel Bottle |
|---|---|---|---|
| Leaching Risk | High, especially with heat or age. | Minimal to none. | Minimal to none. |
| Microbial Growth | High risk, as crevices harbor bacteria. | Lower risk if cleaned properly. | Lower risk, easy to sanitize. |
| Sealing Ability | Varies, but can be effective with a good lid. | Excellent for airtight storage. | Excellent, often with a silicone seal. |
| Taste Effect | Can absorb plastic flavors over time. | Neutral; no taste absorption. | Neutral; no taste absorption. |
| Durability | Prone to scratching and degradation. | Fragile; risks breaking. | Very durable and long-lasting. |
Practical Tips for Water Safety and Storage
To avoid the risks associated with old, stagnant water, follow these simple guidelines. The safest approach is always to use fresh water, but if you need to store it, doing so properly is key.
- Wash Containers Daily: For reusable bottles and glasses, daily washing with hot, soapy water is essential to prevent bacterial and biofilm buildup. Let them dry completely before refilling.
- Use Sealed, Non-Porous Containers: When storing water for more than a day, use sealed glass or stainless steel containers to prevent contamination and chemical leaching.
- Store in a Cool, Dark Place: Keep stored water away from direct sunlight and heat, which accelerate bacterial growth and chemical leaching from plastic.
- Refrigerate If Unsealed: If you are using a filter pitcher or a container that isn't completely airtight, refrigeration will slow bacterial growth significantly.
- Pour, Don't Sip: If you are filling a large container from which you will serve yourself later, use a separate, clean glass for drinking to avoid introducing mouth bacteria into the main supply.
- When in Doubt, Pour it Out: If the water looks cloudy, has a strange smell, or tastes off, do not risk it. Just pour it down the drain and refill with fresh water.
The Breakdown of Tap Water's Disinfectant
Tap water typically contains a residual amount of chlorine to kill bacteria and other microorganisms within the public water system. This is your first line of defense against contamination. However, once the water is exposed to air, this chlorine begins to evaporate. Over the course of 15 days, any chlorine that was initially present will have completely dissipated, leaving the water vulnerable to microbial growth from the air and your own touch. This is a critical reason why tap water that has been sitting out for so long is considered unsafe.
Ultimately, while water itself has an indefinite shelf life, the cleanliness of its container and the environment play a crucial role in its safety. After 15 days, water that has been exposed to air and human contact is highly likely to be contaminated with bacteria and potentially harmful chemicals, especially if in a plastic bottle. The potential for unpleasant taste, biofilm formation, and illness is simply not worth the risk. For peace of mind and health, it is always best to opt for fresh, clean water every time.
Center for Disease Control and Prevention - Flushing Plumbing
