Does water expire? The role of the container
Pure water does not expire. It is a stable inorganic compound that does not support the growth of microorganisms on its own. The "expiration date" printed on many bottled waters is a misnomer, and for many years, the Food and Drug Administration (FDA) has stated that properly produced and sealed bottled water has an indefinite shelf life. However, this indefinite shelf life is only a theoretical possibility under perfect conditions. In reality, the bottle's material and storage environment are the critical factors that cause water to become unpleasant or unsafe to drink over time.
Why plastic is a concern for long-term storage
Most commercial bottled water uses polyethylene terephthalate (PET) plastic. While safe for its intended purpose, PET is not completely inert and is slightly permeable, meaning it can interact with its surroundings. Over time, particularly when exposed to heat and sunlight, the plastic can degrade and leach chemical compounds like antimony and bisphenol A (BPA) into the water. This chemical migration can alter the water's taste and smell, giving it a "plasticky" flavor. A study found that leaving bottled water in conditions of 167°F for five days rapidly accelerated this leaching process. For long-term emergency storage, it is prudent to use BPA-free or food-grade containers and regularly rotate your stock.
The risk of bacterial contamination in opened bottles
Once a water bottle is opened, its pristine, sealed environment is compromised. Airborne microorganisms and bacteria from your hands and mouth can enter the water. While this is not immediately dangerous for most healthy individuals, bacteria will multiply over time, especially in a warm environment.
- For opened bottled water: Consuming it within 4-6 days, especially when refrigerated, is a good practice. Water left in a warm car for hours, where bacteria can thrive, is best avoided.
- For tap water in an open glass: Experts recommend not leaving water out for more than 12-24 hours, as chlorine dissipates and the water can absorb carbon dioxide from the air, creating a stale taste.
Long-term storage recommendations and practices
For emergency preparedness, a long-term water supply is crucial. The Centers for Disease Control and Prevention (CDC) recommends storing at least one gallon of water per person per day for at least three days. When preparing your own supply from the tap, the storage methods are vital.
Steps for Storing Tap Water:
- Choose a Food-Grade Container: Use containers specifically designed for water storage, such as those made from food-grade plastic, glass, or stainless steel. Never use containers that have held toxic substances.
- Clean and Sanitize: Wash the container with soap and water, then sanitize it with a diluted bleach solution (1 teaspoon of unscented bleach per quart of water) before rinsing and drying.
- Store Properly: Keep containers in a cool, dark place, away from direct sunlight and chemicals like gasoline or pesticides, as plastic can absorb vapors.
- Rotate Your Supply: Replace stored tap water every six months for best quality, as the disinfecting chlorine will dissipate over time.
Comparison of water container materials
| Feature | Plastic (PET) | Glass | Stainless Steel |
|---|---|---|---|
| Chemical Leaching | Possible, especially with heat or age. | Negligible. | Negligible, though can react to very acidic substances. |
| Taste Effect | Can impart a "plasticky" taste over time. | Inert, maintains water purity and taste. | Inert, maintains water purity and taste. |
| Durability | Prone to degrading, cracking, or softening with age and heat. | Can break if dropped. | Very durable and resistant to damage. |
| Permeability | Slightly permeable to gases, potentially affecting taste. | Non-porous, excellent barrier. | Non-porous, excellent barrier. |
| Recommended Use | Short-term consumption, avoid high heat. | Best for long-term storage and reuse. | Great for reusable daily bottles. |
How to spot bad water and what to do
Even with proper storage, it's wise to visually and sensually inspect water that has been stored for a long time. The risks of improper storage and contamination are real, so always err on the side of caution. If any of these signs are present, it is best to discard the water.
Signs of Potentially Bad Water:
- Strange Smell: Musty, chemical, or metallic odors indicate contamination or leaching from the container.
- Off Taste: A bitter, stale, or chemical flavor means the water's quality has been compromised.
- Cloudiness or Particles: Any discoloration, cloudiness, or sediment suggests microbial growth or container breakdown.
- Damaged Container: A soft, bulging, or cracked bottle indicates the material has degraded.
In case of suspected contamination, boiling the water for at least one minute can kill most pathogens, though it won't remove chemical contaminants. For long-stored water showing these signs, it's often safer to use it for non-potable purposes like watering plants, as long as it's not severely contaminated.
Conclusion
While the concept of water “expiring” is scientifically incorrect, the quality of water can degrade significantly depending on its container and storage conditions. Unopened, properly stored bottled water can last for years, but the quality of the container, particularly plastic, will eventually decline and affect taste. Opened water is vulnerable to contamination and should be consumed quickly. For long-term emergency storage, food-grade containers made of glass or BPA-free plastic are ideal, with regular rotation every six months recommended for tap water. Paying attention to storage practices and visual cues is the best way to ensure your water remains fresh and safe to drink.
For more information on water safety and emergency preparedness, consult resources from the Centers for Disease Control and Prevention (CDC).
